BayQuilI'm running most games fine with a GTX 670 on 2560x1440. I can max out most games around ~30 FPS. Slightly more modest settings will net you ~50. The 670 and 7950 have pretty similar performance.
BayQuilYou can run most games with a 7950 relatively maxed out. More demanding titles will require you to cut back on anti-aliasing (MSAA,SSAA,etc), though that becomes less of an issue the higher the resolution and you may not really notice it. The FPS requirements to look smooth depend a lot on the game.