Sup? Here's the deal: on average the GTX 670 is 5% slower than the GTX 680. I popped a 680 into my new build last night, haven't gotten to test it out much, BUT I couldn't find a way to make skyrim drop below 60 frames even when being chased by every guard in riften and running to the top of the temple of mara stairs and looking at the market. Battlefield 3, all ultra with 2x MSAA and the card just laughed.... Never below about 55, usually around 70+ FPS when I turned off VSYNC.
Anyway, 670's can be overclocked to be like a stock 680, which is pretty much what I have (a little faster than stock), so you can expect those frames. Good luck! It's a sweeeeeeet card my man. I know that's not exactly the detailed answer you're looking for, but it's a real world trial, which I find more indicative of the real experience.