I recently started doing bigadv smp unit again on my main machine, which is now paired w/ only a single GTX460 instead of the three I used to use. With three of them installed there was no way it could complete most bigadv units in time, because of the massive cpu usage the GPU clients take. But even w/ only a single GTX460 running 912/925 point units, I believe it is still having a rather large performance hit on the TPF of my SMP client.
I have two bigadv machines going at the moment. The one w/ the GTX460 has a 1GHz lead in its CPU clock, yet its TPF is nearly identical to the slower machine. The slower machine using a GPU2 client w/ a 8800GTS. So the GTX460 must have a huge impact on performance of the SMP client. As soon as I finish this WU I am going to stop the GPU client to see how much of an impact it has.