Between Linux 3.2 and Linux 3.5, the OpenGL performance in Nexuiz was relatively flat for the Radeon HD 4650 graphics card when paired with the Mesa 9.0 user-space. With the Linux 3.6 kernel is where the open-source Radeon graphics became faster. Per the Linux 3.6 DRM pull, the Radeon driver beginning with this release is where PCI Express 2.0 support is finally enabled by default. This greater PCI-E bandwidth explains the performance boost for some OpenGL workloads.
For the old OpenArena release, there isn't much change out of any of the tested kernel releases since this older ioquake3 game release is rather lax on the graphics processor.
With the newer OpenArena game release, the Linux 3.6 and 3.7 kernels are faster for the aforementioned reason.