Now this is of course pertaining mostly to Kepler and Fermi.
I have benchmarked in two games the 580 vs the 670.
EVGA GeForce GTX 580 FTW HC2 on air cooling (custom with a factory OC of 850mhz with 4200mhz memory clock.
vs
EVGA GeForce GTX 670 SC reference with a boost clock of 1176mhz and...