Starting with Doom 3, we see that KDE actually is the slowest by default but with its easy suspension of desktop effects on full-screen windows, it jumps into the top spot. GNOME, Xfce, and LXDE all performed well by default and much better than the default Unity environment.
Unity was the slowest for Lightsmark by default while LXDE was the fastest among the stock desktops, but it wasn't by a wide margin. When suspending the KDE KWin effects on full screen windows, the KDE 4.9 performance jumped in front.
When running Nexuiz, the results between the six desktops were very close, but when suspending the KWin effects automatically on full-screen windows, its performance jumped up for the open-source Intel graphics.