ATI won't help you with video encoding, you need nVidia's CUDA for that. That said, switch off CUDA and do some video encoding, you may see that CUDA is actually useless when you have such a fast processor.
For the low end, ATI beats out nVidia completely in gaming performance.
not entirely true, there is avivo for ati
EDIT: with opencl or DirectCompute, we may see a cross vendor app