For the ioquake3-based OpenArena game, and using the 0.8.8 release that makes use of GLSL and other advanced features compared to earlier versions of the rudimentary first person shooter, the performance was competitive between Ubuntu with KDE and Windows. The KDE-based Ubuntu results were basically right in line with the Windows 7 performance for the GT 220, GTX 460, and GTX 680 graphics cards.
Turning to Unigine and their more demanding cross-platform OpenGL tech demos, the performance was also competitive between Windows and Linux when Ubuntu was using the KDE desktop. Unigine does a good job at maintaining quality Linux support within their advanced engine with its OpenGL renderer. The default Ubuntu 12.10 desktop with Unity did lower the results, but KDE was able to show that the open-source operating system could compete with Windows 7 when tainted by the binary driver.