7970 is now equal to the 680 with the 12.11 drivers and the 7970 Ghz edition is even faster.
So I would say get a 7970 and you will be gaming on highest settings for a few years
Check the 7970 X2 review. Admittedly a limited data set, but you're still looking at ~5% gain with the GTX680 across the board. Radeon wins the first few, GeForce wins the others. The GHz edition is indeed faster still, but again by around 5%. The differences we're talking about are negligible anyway - 5% is the difference between 40fps and 42fps. It's hard to justify the added cost of a 7970, GTX680 or 7970 GHz over a GTX670 when the difference is costing you at least £35 for the 7970 and even more for the other two.