One more thing. I think NVIDIA GPUs are using some CPU like how you used to have to leave one core open for AMD. I have a vague recollection of reading this, maybe at https://foldingforum.org/
As anecdotal evidence I present my beleaguered E2160/GT430. I had a few CPU WU's crap out on me and then my GPU OC seemed to be a problem so I stopped Folding on it for awhile. I've recently begun using the GPU again (at a lower clock) and I've noticed that Core_17 keeps my CPU usage at 50% (basically one of the two cores).
I'm wanting to say it has to do with using OpenCL instead of CUDA? I'll look into it more sometime today, maybe.
Oh, also, I found this tool
. I haven't played with it yet. It's a GPU Folding benchmark. Apparently, NVIDIA drivers after 327.2.3 (except on 780, 780Ti, Titan) suffer Folding performance hits. Something to look into if someone is not a gamer, or doesn't need the features included in more recent driver packages.
Found something else cool. CPU and GPU stress tests designed for Folding. https://folding.stanford.edu/home/download-utilities/