First things first - your 750W PSU should be plenty to run two 6970 in Crossfire. Those cards have a maximum TDP of 250 watts, with typical gaming loads around 190-200 watts under full load. Even with a OC on your CPU, your total system output under load is probably under 550 watts.
Your unlocked 6950 MIGHT run Crossfire with a genuine 6970, but only if you're running a 6970 BIOS on the 6950. The driver has to recognize the card as a full 6970 in order to be paired with another 6970.
The 750W Cooler Master GX is a junker:
Although, the Bronze GX units are actually decent and can be trusted. So if you do not have the GX Bronze Series, then you need to replace it before you attempt this.
Anyway, you will need a quality-made 1000-1100W PSU for three 6970s. For two, a quality-made 650-750W PSU is enough. However, I stress quality-made. The non-Bronze 750W GX Series is not to be trusted.
How much can you spend on the PSU?
CoolerMaster PSU's are notoriously unreliable. I typically stick with XFX PSU's. I am a big fan of the brand and most of their PSU's are just Seasonic internals (a well known reliable brand) as well as being decently priced. I feel that are two parts in a PC that should ALWAYS be of known quality and that's your PSU and your CPU cooler.
For two cards you will want around a 750 watt PSU and 1000 watt for three. Newegg actually has the XFX 850 Black Edition (same one I use) on sale and with a rebate right now. I think you can pick it up for a little over $100 after all is said and done. It's fully modular and Gold certified. Pretty much a steal.
The 69xx is a good card man. If I already had it, I wouldn't get rid of it for anything else. No point in spending the money for such a little boost. I think we get too snobbish about frame rates and being able to max settings out to 11 lol. I'd wait until AT LEAST the 8970 came out and them wait 6 months for a decent price drop.
As far as will the different cards work with each other, according to the AMD crossfire chart, it SHOULD work. You have to make sure your MoBo will do 3 cards without going down to 4x though. You'll bottleneck in that instance and will defeat your purpose. 8x is fine as the 6970 won't use it all.
Do it up bro! Get a better PSU and rock those crossfired 69xx's!
OFFICIAL AMD FX-83xx Vishera Owners Club
Haha thanks for the kind words guys, sorry if the post is a little long..... Anyway yes thia psu is bronze gx series maybe I forgot to mention sorry anout that. So if 2 cards ill be ok with this psu then ill hang on to it up until I get 3rd card.as far as budget on a psu I really dont have one,id rather invest more like u guys are saying then buy some junk that will probbly fry my components! maybe around 200 dollars id like to pay for a fullu modular psu.seasonic,corsair,rosewell, what else is good ? Xfx I like the way they make there psus!hopefully better then there gpus lol, no pun intended.yeah i love these cayman gpus they still have quite a bit of punch but dont get me wrong its not like id turn down a 7970 lol,.maybe when prices drop I might pick up a couple? Kinda bumed out about nvidia coming out wulith titan, I cant wait too.see how amds gonna respond to it! There is some fun times ahead thats for sure lol! Thanks guys I.reaaly appricate the advice and help.
What jerrolds is saying is, use paragraphs. When you start a new thought or new subject, start a new paragraph. Your posts are just one giant paragraph and it can be difficult to read, especially if someone is tired but they still want to help.
Anyway, I'm relieved to see that you have the GX Bronze Series. So, I recommend keeping it until you decide to add a 3rd 6970.
Now as far as performance goes what can one expect from running say 3 Radeon 6970s in tri-fire? My goal with this is to be able to run 3 monitors with a resolution of 1920x1080,I play older games such as metro 2033, flight sims,some splinter cell,I like a good racing game but ive yet to see anything on pc that resembles Forza motrorsports they have for xbox 360.I like the customization options and being able to fix-up your car-paint,stickers,wheels,body-kits ect ect....I have dirt 3 which is great but u cant really do much for customizing,can u guys recommend any good games like that?
Re: BIOS, you can use GPU-Z and it will tell you what BIOS you're running, then look it up Google and find out what board/GPU it came off of originally.
For three monitors, three cards will perform extremely well with Eyefinity. I'd estimate 55-70 FPS on all three screens in "most" of the older games. There should be plenty of benchmarks online to verify.