See my reply in the AE forum.
not practically helpful...
anybody running the gtx 680 on photoshop? due to OpenGl and the changes in the design of kempler cards, would the gtx 680 fair worse than a gtx 580?
I always find the benchmarks on this site helpful:
It seems to imply the 680 you're considering is faster than just about everything.
That said, for most things you need only a card that scores 1000 or higher on that benchmark for Photoshop to be fast and fluid. Personally I feel (as an OpenGL software developer myself) that ATI's drivers are of higher quality than nVidia's, and if I were asked for a specific recommendation I'd suggest the VisionTek ATI Radeon HD 7750 or 7850, depending on budget and computer power supply capability.