Interesting - since your post I've found that any credit earned by my CPU is a wash.
A few times I've watched the GPU fold with idle CPU, and when the CPU gets a work unit, thee TPF does increase on the GPU by about 10%. Whatever credit estimate the CPU has, seems to get subtracted from the GPU estimate (proportional to how % complete the processing is).
My system is still burning through with very little involuntary idle time.
Are you looking to upgrade your system? I seriously considered getting all of your equipment at the time it came out (because AMD fanboi) but decided to wait because my Core i7 920/Radeon 7970 was still doing very well with games at 1080p.