balistic2 :
I am also interested in this. I understand that SLI 570s will be better than a single 580, but where does VRAM come into play?
I am contemplating either getting a 2nd 570 classified or sell it and get a 580 classified 3gb. I noticed in the bf3 beta that I was maxing out my VRAM, but I don't know if I was noticing it due to the bugginess of the beta. When you hit the VRAM wall on a 570 classified 1280 mb (not exact), what should happen? Will the 580s extra VRAM be noticeable?
I would like to play at a 1920x1200 res with some sort of AA on.
VRAM comes into play when you are gaming across multiple monitors or when you game above 1080p. Since you only have 1 monitor, playing @ 1080p, you will not notice any difference between 1gb and 2gb and 3gb at all, except MAYBE MAYBE a couple of fps here and there on the MOST demanding titles when you turn up every setting to the max. Otherwise, no, you will not notice any difference.
I honestly would suggest you go with either two 6970's in Xfire or two 570's in SLI. Both options will blow the 580 out of the water and will also be cheaper. The 6970's should provide better performance over the SLI 570's OVERALL, though not by too much, because of better scaling of the AMD cards, but you can't go wrong either way. I would return that 6990 in a heart beat and get your Xfire on.
In the end though, you will not notice a difference in performance between any of the above listed combinations. Me personally, I have a 560ti and I will be just happy with it. It will max just about anything out except the MOST demanding titles.. of which there are maybe 2 and there won't be anything that demanding for a long time to come, so its all good. When the 7900 HD series come out with XDR2 ram and pci-e 3.0, I will sell my 560ti for about $150.. put down another $150 and get myself a truly badass card.