NVIDIA vs. Nouveau Linux Driver Performance With Extra Kepler Re-Clocking Patches
Xonotic at least delivered playable frame-rates at 1080p when using the GTX 680, GTX 760, and GTX 780 Ti, but still it was much slower than the speeds when using the official NVIDIA Linux driver.
BioShock Infinite really wasn't playable on Nouveau given the re-clocking issues. The GTX 750 Ti wouldn't run at all since its OpenGL implementation isn't as featured for Maxwell as Kepler.
There's some bottleneck happening when trying to run DiRT Showdown on Nouveau.