Well, here is the thing, in SINGLE precision floating point, GPU's are quite a bit faster than CPU's. However in DOUBLE precision FP, that is not necessarily the case. A 4P system probably actually has quite a bit MORE DP FP power than a current high end GPU. I dont know the exact numbers off the top of my head. I am not sure if F@H requires DP or if SP is good enough...
They use SP...
The difference to this point has been the type of calculations...