I'd prefer the 7970, but that's because I'd use it in ways that it tends to best the 670. Some other people (possibly such as yourself) might use the 670 in ways that it bests the 7970. For example, I don't care about 3D gaming, but if you did, from what I've read, Nvidia has AMD beat in 3D gaming and that would make the 670 be a better option.
If given the opportunity, I'd use some programs that can make use of the huge Direct Compute and OpenCL advantage that the 7970 has over the 670. The 7970's overclocking advantage would definitely also play a part in my decision.
PhysX wouldn't worry me because if I wanted GPU PhysX, then I'd throw in one of my many spare Nvidia cards to act as a PhysX processing unit for the 7970 and I don't care much for adaptive V-Sync (I prefer Lucid Virtual V-Sync).
If I was to recommend a 670, then I'd probably go for the Zotac AMP! model.