nah, ive never had that problem. it only seems to slow down when i havent done anything for a while and it accesses the disk for some reason or another. overall i love this distro. and as to the ati question...
http://www.ati.com/support/drivers/linux/radeon-linux.html
did you try that
also, ati's official drivers cover all of a range of cards. i.e. their catalyst set (which they just came out with a new version of ... 3.7 i believe) so it doesnt seem all that surprising to me that the linux one would cover a range.
do you have problems with your video, or just want it updated?