You're better off looking at a GTX670 for near enough the same performance interms of frames/second, but massively smoother, more consistent delivery of framerates. Check this out:http://techreport.com/review/23981/radeon-hd-7950-vs-geforce-gtx-660-ti-revisited/3
It's a new way of testing performance, to more accurately represent the 'smoothness' delivered by a card. Frames/second is a crude, oversimplified measure of performance that accurately reflect true smoothness/responsiveness. We'll be seeing a lot more frame latency benchmarking moving forward.
I know these aren't the models you're looking at, but they highlight important differences that are still applicable to GTX670/7970 (since architecturally the GPUs are very similar to those in the review).