You know, I have no idea if not working in a PC would be expected behavior. In the early days of Linux on x86 Macs one advantage of using BIOS emulation instead of EFI boot was the Radeon driver could use legacy calls for video mode selection (not being able to broke the accelerated drivers at the time) but I have no idea if the legacy BIOS being "present" to that extent would translate to the card being usable on a non-Mac.