I have always meant to gather the info and do this but never did.
It needs to be remembered that the other issue with Fermi and other Nvidia cards not used regularly is that they frequently will stay in 2D mode due to throttling not getting triggered properly.
If your Hack id's as "Mac Pro 4,1" or "Mac Pro 5,1" you can edit the AGPM kext to fix this.
It is easy to figure out if you have the issue. Run OpenGl view and check test results.
If you get numbers in hundreds, you need to fix. If numbers start in hundreds then JUMP into thousands, no throttling issue.
The AGPM is a bit of a mystery still. Oddly, the 2 GPUs enumerated in it are the GT120 and the GTX260. SInce the GTX260 was never a "real" mac card, this is very odd. Especially since a GTX285 can throttle itself.