If I were you I'd get a 7950 or wait for a 670, but thats just me. I dont' see a point in paying a premium for a the best when its not that much better. The difference between the 7950 and 680 is 18 percent and its a lot cheaper. The 7970 is a fair amount cheaper as well and is only 6 percent weaker.
It depends a lot on your resolution you game at.