You know, instead of listening to everyone drone on about which card is faster, buy them all and try them out.
I've owned a 7970 Ghz, then a 670, then a 7950, and now I'm trying to find a good 680 used to play with.
The 7970 Ghz was faster than either other card, using 12.8 drivers. The 7950 was not faster than the 670. The 670 was reference, stock, and it still had an average 1fps lead over the 7950 (1000/1250) when I tested it. At 1100/1400, the 7950 is around the ballpark of the 7970 Ghz stock, but then again, I could clock the 7970 Ghz much higher too.
I think the prices are fair, at least what I paid. $360 for 7970 Ghz, $305 for 670 and $300 for 7950.
The thing about this forum is, it's not red biased, it's 7950 biased. At least in my experience, I liked the 670 more than the 7950, but in terms of pure performance, the two are very close.
Once again, I've had both, it only becomes faster clock for clock after you breach ~1050 MHz. Up to then the 670 is still highly competitive. And for a card that drops to its knees... it's doing pretty damn well in both TR and BI, even at 1600p.