I currently have a 7850 and am playing games such as bf3 and crysis however am wanting some more kick, some more fps would be nice. Is the 670 worth buying, is the improvement noticeable ? And how much better is the 680 compared to the 670 even though it is stretching the price (680 is around 300 more than the 670).
7970 GHz Edition is better than 6990. Heck, a good overclocked 7950 is better than a 6990. Good 7950s overclock better than any 6990, so saying something like oh you can overclock the 6990 too doesn't apply.
Flash your GPU firmware and go for broke with an overclock?
+1 and the cgn architecture scales really well when overclocked. I wouldn't drop that much on a gpu when you already have a very good gpu. But hey if you do get a 670, I will gladly take that 7850 off your hands.
Either way, I don't think the cost will justify the marginal performance increase. I think you should just overclock and see what the next or following generation of gpu's bring to the table before you contemplate upgrading.