The fastest desktops for OpenGL gaming with the open-source VDrift racing game were Xfce, Openbox, and LXDE.
KDE was the slowest desktop for the Qfusion-powered Warsow game.
Lastly, for the impressive Xonotic first person shooter game, the fastest desktops were (to no surprise) Xfce, Openbox, and LXDE when using Intel graphics. The slowest desktops with the Ivy Bridge graphics on Linux was KDE Plasma while the default Unity desktop was also receded compared to the other desktop alternatives.
More Ubuntu 13.04 desktop benchmarking from other driver/hardware configurations and an extended selection of benchmarks will be available leading up to the release of the Raring Ringtail.