7970 wins greatly in Maya IIRC, at least with current versions, and Adobe has been working with getting OpenCL supported excellently and has done a good job of it, so even if the 7970 doesn't kick the crap out of the 670 in that, it should still be great. It has far greater dual-precision compute performance than the 670, but single precision can vary between some workloads.
I don't have any of this software, so I'm only going by what I've read/heard, but I've seen a few threads of people using the 7970 in Maya and saying that it was far better than any Nvidia cards for that (although some extremely expensive models might do better, IDK).
7970 especially if you plan to work/play on a multi-monitor setup because amd/ati cards use eyefinity which is way ahead of what nvidia has and the 7970 usually are better in games/photoshop/3D work
so i recommend a 7970 because it can do all the things you want it to and more
yes, seems it is true with premiere pro cs6, however i have only found some news about opencl, Bullet Physics plug-in for maya 2011. So i am still not sure if it actually support opencl or not for the current version.