I haven't been following it lately; but is it pretty easy to install a video card just for boot camp now on the new Mac Pros? I'd love to get a base model with the GT120, but only if it can replace my gaming rig... so I'd want to put a card like that, or maybe a 295, in it for Windows.
I'm running a 2008 2.8 Mac Pro, but it was incredibly easy. Not perfect, but good enough.
My original Apple 8800GT lives in slot 2, and the GTX 275 is in slot 1. When I want to run OS X I unplug the two power leads from the 275 and plug one into the 8800GT, OS X works perfectly and doesn't know the 275 is there.
When I want to run Vista, I unplug the 8800GT and put both power leads into the 275. I transfer the 30" onto one of the 275's DVI outputs and job done. Vista doesn't have a fit over the two GPUs as the 8800GT isn't powered, and is therefore "not there". However, the Mac sees the 8800GT at boot (and hence the EFI ROM) and is happy to get past the chime.
I have set the MP to default boot to Windows, as when booting on the 275 you don't see anything until the Vista load screens. It's a little bit of a pain swapping the power leads/monitor over, but I can deal with that for a working high-end solution. Blows away that Radeon 4870 any day.