Two GTX680's is probably a bit of an exaggeration. I just finished playing the 2nd game with everything at max settings (except ubersampling) at 2560x1440 smoothly on two HD6970's. I'd go as far as saying particular parts of the game such as the forests near the town of Flotsam are some of the most beautiful graphics I've seen in a game in quite some time. Some of the footage from the 3rd game looks absolutely stunning as well.
Well, I was including ubersampling...if you dont mind playing with that setting off, then yes, even a single 480 will suffice with other settings maxed @ 1080p (one of my previous videocards). Theres certain graphical anomalies introduced when using the non-uber in-game antialiasing, so I tend to prefer the uber setting.Like I mentioned, the immediate scenery can be amazing, but the draw distance, and the way the game engine transitions from near to far, isnt so attractive IMHO.But none of these things comes close to ruining an amazing game.