Bought an ASUS EAH6850 to replace the Nvidia cards I was using. Everyone keeps saying how the ATI 6 series is so hard to install and how easy the Nvidia cards are. Well, I tried the 550ti , 660ti, 640 and in all cases, there is some or the other issue with OpenGL -550ti being the worst ever! Then there are all the kexts to be edited for OpenCL, AGPM thresholds etc. Installation with all these cards was easy. But the post-installation requires too much effort only to have a card with bad driver support.
Bought the 6850 for less than what I paid for the 550ti, updated my org.chameleon.boot.plist to ATI specs, shut down, plugged in the 6850 and booted up with no problem at all. No kexts need editing, everything runs perfectly where all 3 Nvidia cards were failing. Games, apps, wake from sleep, resolution changes - everything.
Tried the card with an installation. Only thing needed is to rename the ATI6000Controller.kext on the USB install disk in S/L/E to ATI6000Controller.kext.bak, install, copy the kext from USB S/L/E to your desktop and remove .bak extension - so it becomes ATI6000Controller.kext again and install to S/L/E with a DECENT kext app like kextutility and all is peachy!
You cannot go wrong with this card. All ports even work OOB
Edit: In fact, this card is so well supported that you do not even need to add any enablers or personalities in the org.chameleon.boot.plist. The device Id (6739) is already in all the relevant kext plists by default.