The Nouveau driver on the GeForce GTX 680 at 1920 x 1200 is pushing out just under 60 FPS for the Lightsmark OpenGL lighting benchmark, but the proprietary NVIDIA driver is more than 10x faster with a frame-rate of over 630 FPS.
Nexuiz remains busted for Nouveau on Ubuntu 12.04...
The old OpenArena 0.8.5 that lacks GLSL and other advanced effects is able to run on the open-source Kepler driver at 74 FPS for the 1920 x 1200 resolution, while the closed-source driver for the GTX 680 on the Intel Core i7 Gulftown is still near 600 FPS. It is CPU-bottlenecked on the NVIDIA binary driver.
With the OpenArena 0.8.8 release from earlier this year that now uses GLSL on the ioquake3 engine and other improved rendering effects, the Kepler Gallium3D driver is letting the high-end NVIDIA graphics card operate at just above 44 FPS at 1920 x 1080. The NVIDIA 295.40 meanwhile delivers an average frame-rate of 374 FPS for the HD resolution.