Using an AMD 5770 here and everything is running fine pretty much stays at 60FPS with minor drops of 1-2FPS at 1920x10800 res ( http://i212.photobucket.com/albums/cc189/JDFanning_bucket/Doom3BFG2012-10-1913-04-34-55.jpg ) - what exactly is the problem ? Are you using the newest display drivers and updated Direct3d and OpenGL drivers ? ( Does Catalyst show the http://i212.photobucket.com/albums/cc189/JDFanning_bucket/settings-3.jpg? ))
The problem is framerate that won't go above 20. The proposed cause and solution is this:
We saw this as a result of having multiple consecutive driver installations. You can resolve this issue by wiping the drivers completely and installing the latest driver again.
However, I'm using multiple graphics cards, and I HAVE to have multiple driver installations. This issue shouldn't even exist in the first place.
Edit: Gee, thanks AMD -.- It seems that support of my slave 4850 card was dropped at catalyst version 12.4, so when I updated to 12.8 I discovered that if I want to use my 5870 at the same time I have to run some legacy driver at version 12.6 that encompasses both my cards. So now I'm only running one set of old drivers and everything is working fine...