Are you talking about slowness when running with a composited desktop and unminimizing windows ? If so, there is a "backclear" patch available for the X server which should eliminate the delay. Alternatively, the open source drivers with EXA acceleration will also spped things up.
If the slowness you are talking about is something different, please provide more details or hop over to the ATI/AMD forum on Phoronix where more people can help you with troubleshooting.
