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6850 cf x8/x8 or 6990? - Page 4

post #31 of 43
Quote:
Originally Posted by damric View Post
True for Nvidia SLI, no longer true for Crossfire.
We know you can crossfire the same series of cards, ie 6990+6970+6950 etc. My point is that the higher clock card will down clock to the lesser cards speed. I know this because my 4870 was clocked higher than my 4870x2, and in trifire, all gpu(s) are clocked the the 4870x2 stock speeds. Hence, all cards have to be the same speed, not "all cards have to be the same model", quite a difference
post #32 of 43
Lol @ damric completely missing the point. Its also true on my cards the higher clocked card will downclock to the lower cards clocks. Also op x16 or x8 doesn't even need to be considered the difference is so small, in fact I've seen some tests showing x8/x8 beating x16/x16 in certain games/benches. also here http://www.anandtech.com/bench/Product/302?vs=301 you can see that swapping out your 6850 for 6870's isn't going to be worth the hassle or cost.
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post #33 of 43
Quote:
Originally Posted by damric View Post
This part. That is no longer the case with AMD/ATI cards. The only thing that limits different AMD/ATI cards of the same tier in crossfire is amount of memory. Look it up yourself, or do your own experiments.

http://www.xbitlabs.com/articles/gra...cs_hd5750.html

http://www.xbitlabs.com/articles/gra...s-eah6990.html
I read those articles and didn't see anything supporting this claim. I agree a 6850 will crossfire with a 6870, that's not what I'm questioning.

Quote:
In "effect" in load terms yes but crossfire now, unlike in the past does not auto adjust clock speeds, if you take a 4870 and a 4850 as an example for how it used to be (if I remember rightly they were clock adjusted), both cards would run at the default 4850 (slower) speed, unless of course the user manually adjusted clocks so they were both the same (if that was possible).

Today, if you run a 5870 and a 5850, if they were reference the 5870 will run at 850, the 5850 will run at 725 (of course without manual adjustment), that, as you have pointed out may well lead to one GPU being more loaded than the other, simply because it is slower and therefore having to work harder and/or as you mentioned...... the SP difference? However the benefit now for enthusiasts is that they no longer feel that they are losing that overclock ability in their cards, they can run 2 different models at max overclocks (say 1050mhz for 5870 and 1000 for 5850) and see the performance benefits
I could not find this quote anywhere in those articles. It's actually a TPU forum post. What I can't find is a reputable source or even a tech site that backs up your claims.

http://www.legitreviews.com/article/1107/8/

Legit reviews did an article about 5870+5850. Their GPU-Z tab showed the cards at separate clocks (850 and 725), however in performance the 5870+5850 performed at or below the 5850CF (within 1-3 fps). The article also states:

Quote:
One thing that shocked me was that the CrossFire gaming performance of a Radeon HD 5870 + 5850 was lower than that of a pair of Radeon HD 5850 video cards in CrossFire in all of our testing with the exception of one game. I would assume it is because the higher capacity card (the Radeon HD 5870) gets brought down to the lower one (the Raeon HD 5850) plus some overhead. This basically goes to show that while mixing and matching video cards to run CrossFire works for better performance it isn't the route to take for peak performance. If you want the most from a CrossFire configuration it is clear that you should pair two identical cards together.
I would like it to be true since there would likely be a performance boost if it worked. However, everything I've found says mixing cards in CF still results in forcing the clocks to match.
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post #34 of 43
Thread Starter 
Quote:
Originally Posted by a pet rock View Post
I read those articles and didn't see anything supporting this claim. I agree a 6850 will crossfire with a 6870, that's not what I'm questioning.



I could not find this quote anywhere in those articles. It's actually a TPU forum post. What I can't find is a reputable source or even a tech site that backs up your claims.

http://www.legitreviews.com/article/1107/8/

Legit reviews did an article about 5870+5850. Their GPU-Z tab showed the cards at separate clocks (850 and 725), however in performance the 5870+5850 performed at or below the 5850CF (within 1-3 fps). The article also states:



I would like it to be true since there would likely be a performance boost if it worked. However, everything I've found says mixing cards in CF still results in forcing the clocks to match.
Ok pet rock - I'm giving you the final word on this because you're actually running 2 xfx 6850's.
1. Are you happy with your setup running games at max? (have you tried metro 2033 at max, if so how did 6850cf fare?)
2. My upgrade needs to last at least another year (because my nxt upgrade is a bulldozer, It will be a while b4 I can change card setup again) Do u think 6850? is good for another year?

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post #35 of 43
Quote:
Originally Posted by lazyboyblue View Post
Sorry Forum experts I need some advice.

I was all set to crossfire my 6850 when I discovered that my mobo only supports cf at x8.

I talked it over with the boss (wife) and I have 2 options.

1. stick to the plan - cf 6850 - but at x8.

2. Get a 6990 - but I gotta wait - shes offered one (when bf3 comes out in oct) as a kinda late bd/early xmas gift deal.

What should I do?
Is x8/x8 a no-no?

Cheers in advance guys.
Yea, just XFire the 6850s. After overclocking, they will most likely perform much better than a 6990.

Old advice: Two PCIe sockets are better than one.
    
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post #36 of 43
Thread Starter 
Quote:
Originally Posted by snelan View Post
Yea, just XFire the 6850s. After overclocking, they will most likely perform much better than a 6990.

Old advice: Two PCIe sockets are better than one.
Yeah overclocking, theres another issue. I'm using the standard overdrive at the mo, 850 core overclock, I want to go higher but for the life of me I can't work out how to unlock voltage control on the new afterburner.
    
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post #37 of 43
just crossfire your 6850. you'll be more than happy. anyone want to put up a heaven bench of crossfire 6850's up?
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post #38 of 43
Quote:
Originally Posted by lazyboyblue View Post
Ok pet rock - I'm giving you the final word on this because you're actually running 2 xfx 6850's.
1. Are you happy with your setup running games at max? (have you tried metro 2033 at max, if so how did 6850cf fare?)
2. My upgrade needs to last at least another year (because my nxt upgrade is a bulldozer, It will be a while b4 I can change card setup again) Do u think 6850? is good for another year?

To everyone else
I for one am loving the performance of my crossfire 6850's. My problem with them is noise. The top card idled at ~50C with 50% fan speed before I put on my aftermarket coolers. It was loud enough to bother me while watching movies. But if you're just talking performance, they compete against a single GTX580 very well but can be had for $300 now (~$200 less than 580). http://www.anandtech.com/bench/Product/302?vs=305
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post #39 of 43
Explain this then,

I can run my Crossfire 6850's at different clocks, and one does not magically down-clock to the other. Example: I can run one at stock 775 and the other at 900. The one at 900 does not magically lower itself to 775. You can see this in Afterburner OSD, and if you like, I'll post a screenshot, and benchmarks.
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post #40 of 43
Kinda late in the thread - but I wanted to say that I have been very content with my 68XX series Crossfire setup. The scaling is wonderful, and they perform great. Yes with a slight OC and my tight PCIe slots, they get a bit toasty while gaming. Nothing a nice fan profile can't help. I would say you are in the clear for good gaming performance for at least another 1-2 years as long as drivers keep up.
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