Wanting the 6-core was more of a future-proofing thing. I personally believe that there's no such thing in the PC world, but still, I wouldn't have to upgrade to a newer 6 core when they become more common in a year or two. I bought my Phenom at the end of its life right before the Phenom II 920 and 940 were released, and still regret it.
So, do you think it's safe (meaning the CPU wouldn't be holding anything back) to skip a CPU upgrade and go for a 470/5850? I had always read that with high resolutions (1920x1080) and higher settings, the GPU is doing most of the work, but seeing it at 50% use surprised me...
"Don't fix what isn't broken; Just upgrade it."