Turns out that the 67xx cards are rebranded 57xx cards, and the 6750/5750 are pretty much JUST downclocked 6770/5770s. Since Apple released an official HD 5770, that means we can use those cards when EFI flashed. Here's the details on how I got it to work. You can find second had 6750s on eBay for <$100 (I paid $65 shipped for one) and it's a pretty decent performer. Also, big plus IMO, is that it uses only 1 PCIe power cable. That means many things - first, you save $12+ on the cable. Second, it uses less power, so costs less to operate and makes less heat. Lastly, you can use it with another single connector card (like another 6750) for multi-monitors and cross-fire (in Windows). OK, details. Sorry, no download links for all the apps you will use. You can Google the name and find it all pretty easy. 0) DISCLAIMER: don't do this. You will probably brick your video card and start your Mac Pro on fire. My information applies ONLY to a Mac Pro 4,1 running 10.8.0 with a stock GT120 in slot 1, and a Sapphire HD 6750 Vapor-X 1gb DDR5 card in slot 2. I know nothing about any other devices and I'm not responsible for what you might do with the below information. 1) Set up boot camp, you want Windows for this. 2) Download GPU-Z and check the read-out. The specs should match this more or less: http://www.techpowerup.com/gpudb/249/ATI_Radeon_HD_5750_1_GB.html 3) Use GPU-Z to download a copy of the ROM. Give it a good descriptive name - the exact card and stock, etc. 4) Make a copy of that ROM card and save it on another drive. Just in case. 5) Open up RadeonBiosEditor and load the ROM you just backed up from you card. Change the manufacturer and device IDs using the drop down menus to [EDIT: I HAD TO USE THE VENDOR CODE OF THE ACTUAL GPU MAKER, SAPPHIRE (174B) IN MY CASE, OTHERWISE CARD WOULDN'T WORK IN WINDOWS] ATI/AMD (1002) and HD 5770. 6) Save the modified ROM to a new file, with a descriptive name, like "Sapphire HD 6750 VaporX modded to 5770.rom" 7) Use the program WinFlash to flash you modded ROM to card. 8) Reboot back to OSX and follow this 5770 flashing guide starting at step 2 (NOTE: you have to make a login for the site so you can download the attached files): http://forum.netkas.org/index.php/topic,692.0.html 8a) I took the modded ROM file from my Boot Camp partition and copied it to the root of my user directory and renamed it myrom.rom, per the instructions, and thus making a backup of the rom files at each stage. 9) Open the system profiler and find you new card. There will be a device and manufacturer ID. Make note of that and keep it handy. 10) Once you finish those instructions, you need to update your kexts. Go to \system\library\extensions\ and right click on ATI5000Controller.kext and select Show Package Contents and navigate to Contents and open info.plist with a text editor, I recommend TextEdit. 11) Find the area under IOPCMatch (or something like that) where a bunch of similar strings to your noted device ID are listed. Add yours in to match. Off the top of my head (not at my Mac right now) the ID is 0x68be1002, but DO NOT TAKE MY WORD FOR IT. LOOK IT UP. You'll notice there's an x missing from the vendor ID part of the string, when compared to the system profiler's reported info. Make it match the length and format of the other info in there exactly. Also, don't add any unneeded spaces to the beginning or end of the string. Just one space between each entry. Save and close. 12) Repeat the with AMDRadeonAccelerator.kext and this time search for the word Juniper. Find the similar list of hex device IDs under that section, and add your device ID there. Save and close. 13) Use the program Kext Wizard to repair permissions and rebuild the kext cache. 14) Reboot and plug the cable into the bottom DVI port of the 66750. It should work perfectly. 15) Reboot again and this time reset the PRAM (Cmd-Otion-P-R). This will fix your likely now broken sound output. Results: QE/CI works (as confirmed by Dashboard "ripple effect"), Steam games load (I get 60fps on Portal 2 with 4xAA 8xAF max details on everything at 1680*1050. I accidentally left Vsync on though, so it's capped at 60 - I'll test again without Vsync to see what it can do). No boot screen on DVI. SUPPOSEDLY you can get it via VGA with a DVI-VGA adaptor [EDIT: this works! Boot screen over VGA!], which I will test this weekend. I'll also test to see which ports work, though I don't think I have the correct DP adaptor. I also only have a single monitor so I can't test simultaneous multi-monitor support. PROBLEMS/NOTES: [EDIT: the below was resolved by changing the vendor code, see edit above] My 6750 stopped working in Windows (the GT120 still works fine so you can boot in and do stuff). Worked perfectly with stock drivers (as you'd expect) before flashing, but now fails all together. I tried to uninstall and reinstall the AMD drivers, but that had no affect. Device manager says that Windows has stopped this device because the drivers reported an error, and GPU-Z reports an incorrect memory speed. I am pretty confident I can get it working, though. First thing I am going to try is wiping out my Win7/Boot Camp install and reinstalling it with a 64-bit edition and see if Apple's default installed Windows drivers do a better job with the card, since it's got EFI now. No idea if that makes a difference, but just having a fresh install of the drivers could fix it. If that doesn't work, I have some minimal research suggesting, from the Hackintosh community, that setting the vendor ID to Sapphire instead of Radeon fixes this problem in Windows and doesn't impact OSX. I am assuming that you'd have to modify the kexts to add the new device ID based on the new vendor code. Which brings me to... I did this on OSX 10.8.0, no idea if it works on 10.8.2. But, it should. I expect that I will have to re-edit the kexts, but that takes about 15 seconds. I will update after I make a backup of my boot drive and report back in. Any questions?