KWin Can Cause A Performance Hit Too, But It's Different From Compiz

The Nexuiz frame-rate had actually increased with the Catalyst driver when Compiz was running compared to Metacity, but with KWin there was no performance change. With the NVIDIA driver the performance hit was shared between Compiz and KWin.

The NVIDIA driver experiences less of a performance hit with KWin while running the VDrift racing game where as the Catalyst performance is indifferent again.

When running Enemy Territory: Quake Wars with Compiz we see the Catalyst driver actually losing ground where as the NVIDIA driver surprisingly gains.