A stock vs stock, oc vs oc review comparing the 670, 680, 7950, and 7970 at HardOCP (although they need to bench a few more than 4 games):
http://www.hardocp.com/article/2012/05/14/geforce_680_670_vs_radeon_7970_7950_gaming_perf/4
Quote:
The Bottom Line
NVIDIA has been able to manhandle AMD with each launch this generation. AMD started off strong this year with no competition in sight. NVIDIA was late to the fight, but it did not show up unarmed when it did finally show. AMD has historically held the crown for most power efficient, fast, and affordable GPUs. However, the tides have shifted with NVIDIA's "Kepler" family of GPUs. With the launch of the GeForce GTX 680 and GeForce GTX 670 we have seen NVIDIA trump AMD’s GPU efficiency, performance, and value. NVIDIA even beat AMD to the punch this time with a dual-GPU solution much in part because of the Kepler’s tremendous efficiencies.
It is also worth again noting that AMD has been having trouble this generation keeping up with driver issues and CrossFireX support. For the first four months of the Radeon HD 7970 there wasn't even an "official" driver. NVIDIA on the other hand has been quick to support new hardware with unified drivers at launch of GTX 680. Even with the launch of GTX 690 that driver already supported its next release the GTX 670 so we were able to use publically available drivers from NVIDIA's website for the GTX 670. We've also seen [here] [here] [here] how NVIDIA's SLI is smoother than AMD's CrossFireX, and in every case we've tested so far this generation we prefer SLI over CFX for the best experience. And if you have not been exposed to NVIDIA’s Adaptive VSync Technology, you should give this feature a few moments of your time.
The GeForce GTX 680 represents a tremendous piece of technology that any gamer should love to have in his rig. The GeForce GTX 670 represents what is easily the best value in enthusiast PC gaming GPUs. Pick your poison.
Kyle and I have both been running Radeon HD 7970 configurations in our primary gaming machines for months now and been happy with these solutions. Both of us are now going Green once again.