Sorry for bunping such old thread, but using rEFInd with unflashed PC card is a problematic in Mac Pro system. rEFInd stucking at loading if GOP UEFI card present in EFI UGA system. And what to do is a big question, at least for me...All the boot loaders at boot time require boot screens of course. I suppose you could try to blindly select the correct OS using the cursor and enter keys, but that is problematic.
You could manually change the default OS in each of the operating systems at the command line, but these are non-trivial to do and somewhat risky.
You could install rEFInd, which will make it easier to blindly select a specific operating system. According to the manual all you have to do is hold down the correct key during boot time:
This of course assumes that Linux GPU drivers will even initialize the card. Not sure that they do.
Best thing would be to buy a video card that provides boot screens on a 1,1.