No Clear Winner....
EDIT: The GTX 680 actually turbos to 1058-1110 Mhz, so this is the stock clock used when comparing to a 925 Mhz 7970. Clock per clock is a completely different ball game, and it is important to note because these cards are designed to overclock.
UPDATE: Check here you can see that an overclocked 7970 gets very close and usually passes an overclocked gtx 680 in performance. VR Zone giving the GTX 680 a worse score (8.5, vs 9.0) than the AMD 7970, even given its lower price. Keep in mind the GTX 680 still has a 4.3% OC limit advantage in this specific benchmark. (GTX 680 @ 1335/1800 Mhz AMD 7970 @ 1280/1860 Mhz).
|source: Xbit Labs|
And finally we can compare the performance boost each card gets from overclocking. It’s clear the AMD Radeon HD 7970 benefits more from overclocking in nearly every test both in 1920x1080 and in 2560x1600.
Also seen here, we can see overclocked performance is pretty much a tie! Note the GTX 680 is at 1300+ Mhz, while the 7970 is only at 1125 mhz
This is from techpowerUP
As seen here, we can see across all resolutions the 7970 @ 925 / 1375 Mhz vs GTX 680 @ 1110 / 1502 Mhz we only see a +6% difference. Note to get to the clocks of the 680, the 7970 will have to be overclocked +20.0%/+9.2% for clock/memory.
Now compare these TWO reviews from OCC. they are using identical hardware, and most tests are identical. Watch the 7970 @ 1235/1730 Mhz wipe the floor with the GTX 680 @ 1305/1563 Mhz in most tests.
source 1 - gtx 680 OC
source 2 - 7970 OC
So keep this in mind.
We are actually seeing 1110 Mhz GTX 680s against 925 Mhz 7970s, yet these cards both overclock to about the same Ghz value. Nvidia has the stock crown, while AMD has the overclock crown because its overclocking performance and clock gap is highest. There is no obvious winner in my opinion, yes the GTX 680 is newer, but is it enough? And is it too late?