xorg-server-1.5.1 still sluggish

[Simon Thum]

Markus Strobl wrote:
> A few weeks ago there were some messages about 1.5.0 being sluggish (1-2 second pauses when switching tabs in firefox, delays in menus appearing etc). It looked like the cause was identified and tracked to a patch.
I know that problem very well. I 'fixed' it by switching to git, however 
  with the help of the list I figured enabling DRI has a big impact. 
Maybe that is your problem (probably not if it's a distro build).