I run SLI 570s Twin Frozr III Power/OC edition @ 2560x1600 and the only game I've had issues with its metro 2033 @ max settings on 1600p. Everything else has been butter.

GTX 680 is a good card, but about the price of two 570s which would give higher frame rate. IMO though, I'd get a 2gb 670 and add a 2nd later if you wanted new tech. The 670 will beat a 580.

I think the best thing is to use the 570 and after that, determine if SLI or 680/670 is the way to go.