I have also been experiencing slowdown in general X performance for all the drivers after 195.36.*
This slowdown has nothing to do with composite (composite simply hastens up the process). It also has nothing to do with kde or oxygen.
My setup is enlightenment-DR17 with no composite. 256.x becomes progressively slower if I remain logged on for two days or more. With 195.36.24, I have been logged in for 5 days continuously with zero slowdown.
The following video I made a few weeks ago using 256.53 shows the slowdown: urxvt takes some time to redraw: http://www.youtube.com/watch?v=WIUE4asXqME
Although it is not in the video, switching windows using alt-tab and switching desktops are also not smooth.
Just for the record: Xorg version 1.7.7