Nexuiz is a bit of a different story as its graphics are more demanding and is derived from the DarkPlaces engine rather than ioquake3. With Nexuiz and the Radeon Gallium3D driver, the R300g R500-based graphics performance drops quite severely while the R700-based GPU with the R600g driver still has a small frame-rate increase under Compiz. The Evergreen family's HD 5450 with the R600g driver had the same frame-rate.
The Catalyst driver continued to run at the same speed.
With the Nouveau Gallium3D driver running Compiz had led to a small drop in performance, as did the proprietary NVIDIA driver.