The thing about the 1 gig of textures on the 7950GX2 is that textures don't really amount to much better performance. The main limitations on performance for video cards relate to core and memory speeds, pipelines, and such. The amount of memory for textures will maybe make a 1-2% difference, but it should never be a deciding factor. Tom's has a good article on Video Cards that go more into depth (I think it's Tom's, I read so many review sites they're all merging together...)
With ATI, you can also run AA with HDR, which some people find important. Also, its arguable that ATI has better image quality, but I haven't really seen that for myself. Crossfire is more complicated than SLI, but I doubt you'll be going that route...
Another thing is, with the 7950GX2, you need driver support for games. Not all games support SLI, so if NVidia doesn't have support for those games, than basically all you have is a 7900GT. There are a good number of games with SLI support, but just another warning about the 7950GX2.