Yes it could do it easy 60fps.
No at 1080p a single 680 only gets 30fps unless you turn ubersampling off
Two 780 can.
It was a mis-type, I ment 780. a 780 can easy do 50-60 and 65 depending what going on in the game.
Enough. That's how many per second.What fps does 780 SLI get for Witcher 2