I'm not up-to-date on the performance of AMD CPUs, but the "CPU bottleneck" problem is related to scene preparing, like computing where all the objects are, including objects which move (like AI or thrown). But once the the scene is completely fed to the GPU, it's rendering time is affected by number of polygons, resolution, AA and more. So with a weak CPU, you could still benefit from a powerful GPU if you have a large screen (or even a 1280x1024 with 4x AA).
The idea is not "if" it's bottlenecked by CPU, but "how much" performance is wasted on the GPU.
I just looked for benchmarks, and here is a Guru3D
which benchmarks the 6970 with an Athlon II x4 645 (the 3850 seems to be compared to 635, so it would be just a little slower). As you can see, the higher the resolution, the less the CPU matters. But the testing is done at 4xAA (or more).
PS: Does you friend have a Intel CPU?