I am not sure if anybody tried to enable QE/CI for ATI5970 in MountainLion. The card has been working great since Snow Leopard to Lion. The only thing need is just a modification of ATIRadeon5000Controller.kext by adding the cardID and VendorID in IOPCIMatch as "0x689C1002". Mountain Lion always installs fine. I use xMove and modified the ATIRadeon5000Controller.kext in the Installer before start the install. And it boots fine into Mountain Lion.
The only problem that I have is the QE/CI (QE/CI was enabled in the Lion and SnowLeopard). From my reading so far, it looks like I need to add the card ID and vendor ID to the AMDRadeonAccelerator.kext. But ATI5970 belongs to Class Name "Hemlock" which is not listed in the AMDRadeonAccelerator.kext. I tried to add it to the Cypress IOPCIMatch key, but doesn't work out for me. It stuck after [iOBluethController] Started, which i think it's related to that change.
Can anyone share some light into this? It's kinda frustrated when QE/CI is not enabled (feels like screen got torn sometimes)