You need to dedicate CPU cores to get it upto 99%
For upto 3 GPU's you should use 2 CPU cores
For 4 GPU's you need 4 cores
Mine don't
I have 3 670s running along with a 3770k. The GPUs are all running at 99% and I haven't dedicated any cores to them - I just let Windows do its stuff.
I did try dedicating cores specifically but all I found was that it impacted my SMP PPD negatively.
what are your ppd on CPU?