Overclock.net › Forums › Graphics Cards › AMD/ATI › Crossfire question
New Posts  All Forums:Forum Nav:

Crossfire question

post #1 of 18
Thread Starter 
I'm thinking of getting another one of my HD6950 GPUs to run in Crossfire.
  1. What kind of performance gain am I looking at from running two of these instead of one? Is it worth buying a second over an entirely new single GPU? (Bearing in mind I would have to buy a new waterblock for either option as I watercool)
  2. Also, from what I can tell, when you use Crossfire or SLI, the PCI-E "lanes" go from x16 to x8 each, is that not.. bad? why don't motherboards now let them both run at x16? wouldn't that make them both "faster/better"? or is the performance gain from using 2x cards bigger than the loss of speed going from x16 to x8? (I really don't understand this stuff so excuse my ignorance if it sounds dumb)
  3. Also if I get another card is there a rule like they both have to be running at the same clock speeds if you're overclocking, what happens if they're not?
  4. Which card should be used as the primary one outputting to your monitor?
  5. If you also output to a TV, should you stick that cable in the second card or keep it in the first aswell? (which one is the 'first', the top one?)
  6. Bridges. My card has two connectors for bridges, some googling tells me that you should use only one bridge with two cards and using two might even cause a degredation in performance, how much of that is true?
  7. Does it matter which connections you use, IE, the ones closer to the rear of the case or the front?
  8. Are there "better" after-market bridges or are the ones supplied with the cards perfectly fine?


Thanks and +reps in advance.
Edited by paradoxum - 12/5/12 at 11:28pm
post #2 of 18
a better option is to sell the HD 6950 and get the HD 7950 OC or HD 7950 boost. At the same clocks HD 7950 is 3 - 6% slower than HD 7970 .

http://hexus.net/tech/reviews/graphics/34761-amd-hd-7950-vs-hd-7970-clocks/?page=2

overclock the HD 7950 to 1.1 Ghz and it matches HD 7970 Ghz. HD 7950(1.1 Ghz) is faster than HD 6950 CF. also you get the consistency of a single GPU. no microstuttering and other CF issues like scaling or profile availability. HD 7950 is also cooler and quieter. add to it you get some of the best games of this holiday and its a no brainer.

Gigabyte HD 7950 OC with the windforce3x cooler is a good option.
http://www.novatech.co.uk/products/components/amdradeongraphicscards/amdhd7950series/gv-r795wf3-3gd.html
http://www.overclockers.co.uk/showproduct.php?prodid=GX-098-GI&groupid=701&catid=56&subcat=1673
Fragbox
(14 items)
 
  
CPUMotherboardGraphicsGraphics
Intel Core i5 2400 DH67BL AMD Radeon HD 6900 Series XFX HD 6950 2GB 
RAMRAMHard DriveOptical Drive
Corsair Corsair DDR3 1333 Mhz 2 GB Corsair DDR3 1333 Mhz 2 GB Western Digital Caviar Green SONY DVD-RW AD-7260S 
OSMonitorKeyboardPower
Windows 7 Professional 32 bit BENQ G2420HD Logitech K200 Seasonic VX550 psu 
CaseMouse
ANTEC 200 V2 Logitech mouse 
  hide details  
Reply
Fragbox
(14 items)
 
  
CPUMotherboardGraphicsGraphics
Intel Core i5 2400 DH67BL AMD Radeon HD 6900 Series XFX HD 6950 2GB 
RAMRAMHard DriveOptical Drive
Corsair Corsair DDR3 1333 Mhz 2 GB Corsair DDR3 1333 Mhz 2 GB Western Digital Caviar Green SONY DVD-RW AD-7260S 
OSMonitorKeyboardPower
Windows 7 Professional 32 bit BENQ G2420HD Logitech K200 Seasonic VX550 psu 
CaseMouse
ANTEC 200 V2 Logitech mouse 
  hide details  
Reply
post #3 of 18
Thread Starter 
thanks but as I said I watercool and would need a new waterblock aswell, and that makes your option a lot more expensive especially if I can't sell my card. any one else have opinions?
post #4 of 18
Quote:
Originally Posted by paradoxum View Post

thanks but as I said I watercool and would need a new waterblock aswell, and that makes your option a lot more expensive especially if I can't sell my card. any one else have opinions?

whats the best price at which you are getting HD 6950. you are going to buy a waterblock for the new HD 6950 also. so that cancels out with the waterblock for HD 7950. looks very difficult to find a HD 6950 2GB below 150 bucks. it should be easy to sell the existing HD 6950 and its waterblock for 120 bucks. so in fact the HD 7950 with waterblock would work out cheaper.
Fragbox
(14 items)
 
  
CPUMotherboardGraphicsGraphics
Intel Core i5 2400 DH67BL AMD Radeon HD 6900 Series XFX HD 6950 2GB 
RAMRAMHard DriveOptical Drive
Corsair Corsair DDR3 1333 Mhz 2 GB Corsair DDR3 1333 Mhz 2 GB Western Digital Caviar Green SONY DVD-RW AD-7260S 
OSMonitorKeyboardPower
Windows 7 Professional 32 bit BENQ G2420HD Logitech K200 Seasonic VX550 psu 
CaseMouse
ANTEC 200 V2 Logitech mouse 
  hide details  
Reply
Fragbox
(14 items)
 
  
CPUMotherboardGraphicsGraphics
Intel Core i5 2400 DH67BL AMD Radeon HD 6900 Series XFX HD 6950 2GB 
RAMRAMHard DriveOptical Drive
Corsair Corsair DDR3 1333 Mhz 2 GB Corsair DDR3 1333 Mhz 2 GB Western Digital Caviar Green SONY DVD-RW AD-7260S 
OSMonitorKeyboardPower
Windows 7 Professional 32 bit BENQ G2420HD Logitech K200 Seasonic VX550 psu 
CaseMouse
ANTEC 200 V2 Logitech mouse 
  hide details  
Reply
post #5 of 18
Quote:
Originally Posted by paradoxum View Post

I'm thinking of getting another one of my HD6950 GPUs to run in Crossfire.
  1. What kind of performance gain am I looking at from running two of these instead of one? Is it worth buying a second over an entirely new single GPU? (Bearing in mind I would have to buy a new waterblock for either option as I watercool)
  2. Also, from what I can tell, when you use Crossfire or SLI, the PCI-E "lanes" go from x16 to x8 each, is that not.. bad? why don't motherboards now let them both run at x16? wouldn't that make them both "faster/better"? or is the performance gain from using 2x cards bigger than the loss of speed going from x16 to x8? (I really don't understand this stuff so excuse my ignorance if it sounds dumb)
  3. Also if I get another card is there a rule like they both have to be running at the same clock speeds if you're overclocking, what happens if they're not?
  4. Which card should be used as the primary one outputting to your monitor?
  5. If you also output to a TV, should you stick that cable in the second card or keep it in the first aswell? (which one is the 'first', the top one?)
  6. Bridges. My card has two connectors for bridges, some googling tells me that you should use only one bridge with two cards and using two might even cause a degredation in performance, how much of that is true?
  7. Does it matter which connections you use, IE, the ones closer to the rear of the case or the front?
  8. Are there "better" after-market bridges or are the ones supplied with the cards perfectly fine?
Thanks and +reps in advance.

Performance wont quite double, but a lot of games use crossfire quite effectively. Google benchmarks for your favorite games, and they should list performance between single and dual cards.

Most boards, and definitely yours, will go from x16 to x8/x8 when going to crossfire. This is perfectly fine and minimal decrease in performance occurs from x16 to x8.

When overclocking, both cards will run at the slowest speeds, so if your second card doesnt OC well, your first card wont run as well as it used to. Using one crossfire bridge is more than enough.

Use the top card for your monitor(s). If you want to run eyefinity, all 3 cards need to be plugged into the same card. I am pretty sure that when your cards are set in crossfire, any monitors you plug into the 2nd card wont even work.

The bridge that comes with the cards are perfectly fine. The only time you would want to replace them is for aesthetics (i am not sure if there are nicer looking xfire bridges, but some companies have cooler looking SLI bridges) or if the one you have isnt long enough.
post #6 of 18
Thread Starter 
Quote:
Originally Posted by raghu78 View Post

whats the best price at which you are getting HD 6950. you are going to buy a waterblock for the new HD 6950 also. so that cancels out with the waterblock for HD 7950. looks very difficult to find a HD 6950 2GB below 150 bucks. it should be easy to sell the existing HD 6950 and its waterblock for 120 bucks. so in fact the HD 7950 with waterblock would work out cheaper.

Is this the card you are talking about? http://www.valuebug.co.uk/ProductDetails.aspx?PID=22193
According to EK they have no waterblocks for it and don't plan to make any: http://www.coolingconfigurator.com/step1_complist?gpu_gpus=848

Quote:
Originally Posted by yanks8981 View Post

Performance wont quite double, but a lot of games use crossfire quite effectively. Google benchmarks for your favorite games, and they should list performance between single and dual cards.
Most boards, and definitely yours, will go from x16 to x8/x8 when going to crossfire. This is perfectly fine and minimal decrease in performance occurs from x16 to x8.
When overclocking, both cards will run at the slowest speeds, so if your second card doesnt OC well, your first card wont run as well as it used to. Using one crossfire bridge is more than enough.
Use the top card for your monitor(s). If you want to run eyefinity, all 3 cards need to be plugged into the same card. I am pretty sure that when your cards are set in crossfire, any monitors you plug into the 2nd card wont even work.
The bridge that comes with the cards are perfectly fine. The only time you would want to replace them is for aesthetics (i am not sure if there are nicer looking xfire bridges, but some companies have cooler looking SLI bridges) or if the one you have isnt long enough.

I should first mention that my motherboard is going to be an Asus Maximus V Formula, not the one in my sig, i'm buying a whole new rig. CPU will also be an i7 3770k
Thanks for all the answers. It seems like I should just stick with my unlocked/overclocked 6950 (6970 equivelant or better with overclocks) for the time being.
Edited by paradoxum - 12/6/12 at 6:46am
post #7 of 18
Quote:
Originally Posted by paradoxum View Post

Is this the card you are talking about? http://www.valuebug.co.uk/ProductDetails.aspx?PID=22193
According to EK they have no waterblocks for it and don't plan to make any: http://www.coolingconfigurator.com/step1_complist?gpu_gpus=848
I should first mention that my motherboard is going to be an Asus Maximus V Formula, not the one in my sig, i'm buying a whole new rig. CPU will also be an i7 3770k
Thanks for all the answers. It seems like I should just stick with my unlocked/overclocked 6950 (6970 equivelant or better with overclocks) for the time being.

Either way, x8/8 vs x16/x16 isnt going to be a huge deal. I know its not what you asked, but you may also want to consider waiting until Haswell is released to upgrade your rig. You likely won't see much improvement going from a 2500K to a 3770K for gaming, especially on a single card.
post #8 of 18
I have cfx 6950's. My benches are as good or better than most any 680/7970 single card I have seen. (granted my cards both clock well into 1ghz) So if you can get a good price on a adding a 6950 that's a solid choice.

Personally, I would just sit on the purchase until the 8000 series releases, 3 months?, then look at going that route. I plan on setting up a haswell / AMD 8000 rig in the summer. That should keep me happy for the next 4 years.
Project Haswell.
(17 items)
 
  
CPUMotherboardGraphicsRAM
i7-4770k Asus Maximus VI Hero EVGA 980ti FTW G.Skill Trident X 2400Mhz 
Hard DriveHard DriveCoolingCooling
Samsung 840 pro Samsung Spinpoint F3 1TB Raystorm Block RX360 Extreme, RS 240 
CoolingOSMonitorKeyboard
Pump D5 Vario  Windows 10 Pro Q-nix 1440p Logitech G-710 
PowerCaseMouse
Corsair 750w Thermaltake Core x9 Snow Edition Logitech G500 
  hide details  
Reply
Project Haswell.
(17 items)
 
  
CPUMotherboardGraphicsRAM
i7-4770k Asus Maximus VI Hero EVGA 980ti FTW G.Skill Trident X 2400Mhz 
Hard DriveHard DriveCoolingCooling
Samsung 840 pro Samsung Spinpoint F3 1TB Raystorm Block RX360 Extreme, RS 240 
CoolingOSMonitorKeyboard
Pump D5 Vario  Windows 10 Pro Q-nix 1440p Logitech G-710 
PowerCaseMouse
Corsair 750w Thermaltake Core x9 Snow Edition Logitech G500 
  hide details  
Reply
post #9 of 18
Thread Starter 
Quote:
Originally Posted by yanks8981 View Post

Either way, x8/8 vs x16/x16 isnt going to be a huge deal. I know its not what you asked, but you may also want to consider waiting until Haswell is released to upgrade your rig. You likely won't see much improvement going from a 2500K to a 3770K for gaming, especially on a single card.

Haswell? what socket is that? I have already bought the CPU but I still have time to cancel the order. and how long are we looking at before those come out? and for an equivelant "Haswell" to an i7 3770k, how much $$$ difference is there going to be?

Edit:
Answered my own question, it's socket 1150 and not 1155, which means i'd need to wait for a new motherboard aswell.

Also Wikipedia says:
Quote:
Intel is expected to release CPUs based on this microarchitecture around March to June 2013 according to leaked roadmaps.

That's a long time to suffer with my crappy laptop.. but if you think I should really not buy an i7 3770k and wait for this Haswell CPU?

Wikipedia also says:
Quote:
Compared to Ivy Bridge (expected):

At least 10% CPU performance increase.[6]

Is 10% worth the wait? Especially when I plan to overclock the the crap out of my 3770k as much as possible with my watercooling?
Quote:
Originally Posted by nicedart View Post

Personally, I would just sit on the purchase until the 8000 series releases, 3 months?, then look at going that route.That should keep me happy for the next 4 years.

I think I will do this then, and with regard to my GPU question, I think i'll stick with what I have until then. My 695(7)0 overclocked takes pretty much anything I can throw at it right now anyway.

So in conclusion, I think it's best to stick with the i7 3770k, and wait for the 8000 series cards, any thoughts on that, good idea or?
Edited by paradoxum - 12/6/12 at 7:38am
post #10 of 18
Quote:
Originally Posted by paradoxum View Post

Haswell? what socket is that? I have already bought the CPU but I still have time to cancel the order. and how long are we looking at before those come out? and for an equivelant "Haswell" to an i7 3770k, how much $$$ difference is there going to be?
Edit:
Answered my own question, it's socket 1150 and not 1155, which means i'd need to wait for a new motherboard aswell.
Also Wikipedia says:
That's a long time to suffer with my crappy laptop.. but if you think I should really not buy an i7 3770k and wait for this Haswell CPU?
Wikipedia also says:
Is 10% worth the wait? Especially when I plan to overclock the 3770k as much as possible with my watercooling?
I think I will do this then, with regard to my GPU question, and stck with what I have until then. My 695(7)0 overclocked takes pretty much anything I can throw at it right now anyway.
So in conclusion, I think it's best to stick with the i7 3770k, and wait for the 8000 series cards, any thoughts on that, good idea or?

Why would you be suffering with your crappy laptop? Did you sell your 2500K? If you no longer have a 2500K + Asus motherboard, then the 3770K is a nice chip, but you are likely only getting 10% or less increase from the 2500K to the 3770K. I am stating I would stick with your 2500K until haswell comes out to upgrade, unless obviously you no longer have the 2500K in your sig rig.
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: AMD/ATI
Overclock.net › Forums › Graphics Cards › AMD/ATI › Crossfire question