I bought 2 EVGA GTX 580 3GB to replace 2 XFX HD5970 2GB. The problem with the HD5970, at least in my case, is that they don't have enough memory. 1 GB per GPU isn't enough for Eyefinity, or NV surround. The 5970s performed better at single screen resoltuion that the 580s do, but once you get it up to where I'm gaming, 5760x1080 then that 3GB really helps. A heck of a lot of games, even at this res. use more than 2GB of RAM. So, if you're hoping to max out every game you own, the 3GB 580 is where it's at. The ATI 2GB 6950s and 6970s would be fine for most games, but I'll give you some benchmarks, this is just averages nothing specific.
Far Cry 2, which I couldn't even play with ATI cards at Eyefinity without crahsing
5760x1080 4x AA 55-60 fps average, low being 50 under any conditions 1.3 GB Vram used
5760x1080 8xAA 50-60 fps average, low being about 45 2.2 GB Vram used
Crysis 5760x1080 maxed with 0xAA 45 fps average 1.4 gb Vram used
Crysis 5760x1080 8xAA 30 fps average 2.3 gb Vram used
Fallout New Vegas 5760x1080 maxed 8xAA 60 fps average 1.5 gb Vram used
I thought AvP was ridiculous, you'll see what I mean
Aliens Vs. Predator maxed 5760x1080 4xAA 2.8 gb Vram used 60fps average
I can't remember anything else off of the top of my head, and I'm using v sync on all these games, where with 1gb or less of RAM you couldn't dream of running v sync above single screen res. So yeah, if you're running triple screen the 3gb 580s kick ass. Runs any game I have maxed out, but in some cases lower AA. I have just about any newer first person shooter, rpg and racing game you can think of.
Edited by cerealkeller - 5/22/11 at 4:25am