I'm using bios I got from MSI for my cards with GOP/UEFI support.
Not sure what you meant by that last part? My cards require different bios because they are physically different cards.
I mean are you just flashing them with atiflash or something like that?
I have never been able to flash any bios of any sort onto my XFX Black Edition 7970 Rev 3.1 with the utilities other people have posted on the web. Not even the bios that's on the card already.
Perhaps you are in a different situation where you are just bypassing the digital signature, but I have literally not been able to even do the flashing part.
If you are past that part I have nothing I can help you with since I have not gotten past that part
EDIT:
It seems I have interpreted your title and question wrong, my apologies.