"I'm using a Gigabyte (Radeon) 6870 OC card in my Mac Pro 3,1 that I have flashed in the Mac environment with instructions gleaned from forum.netkas.org/index.php/topic,1085.0.html
(The 6870 is a lower-power (and slightly lower performance) version of the 5870)
Before the flash everything worked except the Apple DVD Player, after the flash the DVD Player is working fine. It's an EFI only flash, however it does kill one of the DVI Ports on the Gigabyte card. I now have one DVI Port, one HDMI port and two MDPs.
I replaced an Apple branded Radeon 4870 and the machine seems snapper. I am not a gamer. I'm attaching two attachments. They came from Apple System profiler. The first is the Graphics Card information, both from my old card in OS 10.7.1 and the new card in OS 10.7.2. I'm also attaching the PCI card info.
I'll post the ASP attachments later. (As I mentioned in the post on the 6870 rom back in mid-August, I saw some flashed 6870s on fleabay. Expected that after the rom was posted.)