With my new brand spankin' new Mac Pro what graphics cards can I put in, is there a restriction?
Not all your vid cards need to contain a mac compatible efi firmware. You should have at least one in your system for start up tasks (like booting in verbose mode)
I have a new nehalem macpro. I use the stock gt120 in slot 2 so it has an efi firmware card in the machine to do start-up tasks. In slot 1 i currently have an asus en9600gt silent. I use NVdarwin.kext to fire up the 9600 at login. I have 2 dell 1080p 24in on the 9600gt and another 1080p on the gt120. Really nice setup.
I have tried this with a 9800 as well, same result. I have also removed the efi card (gt120) and put a 9600 and a 9800 in. Boots fine, just no video until NVdarwin.kext loads just before login