Two 570GTX here,
I play in single 570GTX because in sli mode have 50% more fps
but the game is NOT SMOOTH (there is a very strage kind of long stuttering which I can not explain in writting - it is just not smooth gameplay).
Ofcourse the new patch will fix all that... in xx weeks (add the number of your liking)
Oh, I would not buy a card with onl 2Gb VRAM (which is the 680GTX)
So if I were you, I would wait until September for the real performance card of NV.
~S~