If you continue to ask me how a GPU performs, I will continue to just show you benches, write a few comments, and tell you to decide for yourself lol.http://www.anandtech.com/bench/Product/555?vs=598
Imho, do not buy a GTX 680 over a GTX 670 because the premium in price is not worth the marginal performance gain. But is it a faster card? Definitely. I'd say if you are considering a 27-inch monitor upgrade, then 2560 x 1440 gaming would benefit with a GTX 680. But at 1920 x 1200, meh imho.
The Radeon 7970 is cheaper than a GTX 680 and probably a little faster than a GTX 670. If you ask me to pick between a Radeon 7970 and GTX 670, I'd still say the 670 because the difference will probably be negligible and because I am partial to nVidia with the GPUs out now. However, I can't argue that the Radeon 7970 is probably a better buy than the GTX 670.
When you get into the Radeon 7970, GTX 680 and GTX 690 territories, you are really dealing with monitor resolutions above 1920 x 1200 and multiple monitor setups. Or you are going for benches or wanting to game at 120 FPS on a 120 Hz monitor. Or you just want the best no matter the cost. Somone correct me if I'm wrong