Hmm. Not so sure on that.

I'm running on Ibex 64-bit with the 177.80 driver with a 9600 GT
You are right about the CPU vs GPU balance.
My PC turned into a sloth for a day.
Towards the end of the day I suspended the CPU wus and the GPU progress was much faster.

I have paused the GPU work for the moment because I need to use my GPU workstation over the weekend.