I'm being a bit silly, I know the 670 overclocks , it's just that I've not seen any user benches which show the 7950 overclocked to contend with the 670. If there was a thread similar to the 7850 I may believe you all.
Can't remember where, but I did see some benches comparing massively overclocked 660Ti/670/7950.
It was neck and neck with the 7950 and 670, but with the clocks they used (~1200mhz on 7950 ~1320mhz on 670) you are far more likely to hit those on the 7950, its very marginal on what 670's will hit a good 1300mhz+ clock and even those that do tend to be the higher end cards (windforce, FTW etc...)