The 6.3.19 client is still not quite right. It is not letting the GPU and CPU's to play well together. This might be a Windoze only problem. My Linux64 box seems to be running fine with 4 CPU + 1 GPU tasks running, with the GPU using only 1-2% of CPU time....
I have to check my Win64 box this afternoon.
And it might be a 32bit OS problem...?