Nouveau Linux 4.14 + Mesa 17.4-dev vs. NVIDIA
Even with these three GPUs being re-clocked to their highest (0f) performance state, BioShock Infinite is one of the games still running very slowly with Nouveau.
Dota 2 with OpenGL runs at less than half the speed of the official closed-source NVIDIA Linux graphics driver. What's sad is the relative performance for Maxwell 2 / Pascal GPUs is even much worse than these results due to being bound to their boot frequencies without re-clocking support on Nouveau at this time.
ET: Legacy is one of the lightweight OpenGL games that can run close to the NVIDIA Linux driver performance levels when the Maxwell 1 / Kepler GPUs are re-clocked.