The NVIDIA vs. Open-Source Nouveau Linux Driver Benchmarks For Summer 2018
The ET: Legacy game that's letting RTCW: Enemy Territory live on as open-source and with a more modern OpenGL renderer ran great with Nouveau on Kepler where the GTX 680 came in at 89% the speed of the proprietary NVIDIA 396 series driver.
The lightweight OpenArena game too, obviously, could run well on the re-clocked NVIDIA hardware.
When re-clocked, the open-source Tesseract game ran great on the NVC0 Gallium3D driver and was within striking distance of the NVIDIA 396 driver for the GTX 680 and GTX 780 Ti.
Xonotic also runs well on Nouveau, at least for Kepler/Maxwell1.