I'd second that thought by twoodcc -- I'm not even aware of the OSX client being able to recognize GPUs -- my 285 GTX isn't recognized even though the client knows about the CUDA cores.
And, OK, I know we're a Mac forum here but I have to admit that for the money, a Windows box with a decent GPU can really pull in the points.
Case study:
2010 base Mac Pro 4-core gave me about 11 K PPD
2010 6-core Mac Pro nets about 27 K PPD
I take the Xeon chip out of the base Pro and build a Windows box with it... and I get about 11 K PPD. Now I add an EVGA 560 Ti GPU card (about $220) and that card alone pulls in 19 K PPD for a 30 K PPD total just on the Windows box.
Granted, it is crude and noisy and now lives in the (cool) basement.
Once the weather heats up here I'll have to stop folding on the Pro anyhow...