if the HD 7970 is crossfired, then it will eat a single 670 for lunch and beat out GTX 690.
Not alot of comparison on crossfired, but here are some SINGLE card performance. I think your friend is using the HD 7970 non ghz edition:
+5% ish for special edition cards
More here, I don't want to spam pagehttp://kotaku.com/5964022/the-best-graphics-cards-nvidia-vs-amd-current+gen-comparison