As has been discussed in about a dozen different places (yes, these forums do have a search feature):
- NVIDIA PC cards are supported with 10.7.4 + web driver from their site, or 10.8 out of the box.
- These cards work fine in a MacPro4,1.
- These cards support CUDA.
As always, stock PC cards will not have a boot screen, but work fine once you've gotten to the desktop.