I thought the biggest advantage of the nVidia web drivers was that it enables PCI-E 2.0 transfer speeds (i.e. kicks it into high gear, so to speak) @ 5.0GT/sec transfer speeds for non-EFI Cards. Useful for Texture copying, CUDA, etc...
Since his card is already a "Mac Edition" with the proper EFI, shouldn't the card already be running at 5.0GT/sec speeds? As mentioned, some have had issues with the Webdrivers doing some unexpected things (due to bugs) with certain softwares....
As stated above, you can indeed install the nVidia Webdrivers, and are then boot-time software selectable. Might be your best bet - and therefore have the option to flip back to the Apple Drivers if you run into any issues.