I had similar problems with Ubuntu on my old x850xt, I think its a problem with these cards.
Have you also changed the refresh rates for vertical and horizontal? They are somewhere in the xorg.conf file, this sometimes causes problems if you dont set them correctly.
Have you read this post in the Ubuntu forums? It helped me a while ago.
http://ubuntuforums.org/showthread.php?t=190133
Have you also changed the refresh rates for vertical and horizontal? They are somewhere in the xorg.conf file, this sometimes causes problems if you dont set them correctly.
Have you read this post in the Ubuntu forums? It helped me a while ago.
http://ubuntuforums.org/showthread.php?t=190133