From what I can tell, the 670GTX is slightly faster than a 760GTX and here in the UK it's about £25 cheaper too! I am 95% sure that I'll be getting the 670GTX Zotac next week, because although I do prefer ATI(AMD) as a rule, the 7950 seems a little slower at stock and I don't think the i5 Haswell I'll be buying at 3.3Ghz will be able to max a stock 7950, so OC'ing it would probably be pointless.
An i5 Haswell will not bottleneck a 7950........