While the GeForce GTX 750 series have been around since 2014, using this early open-source development driver stack from 2016 still leaves a lot to be desired due to the rudimentary Maxwell support level in Nouveau.
When booting to Ubuntu 15.10 with the Linux 4.5 and Mesa 11.2-devel dropped in, first up there is still a lot of text corruption with the GTX 750. The GTX 750 also couldn't mode-set to 4K via HDMI so I had to switch to using DisplayPort; see yesterday's 4K HDMI Appears To Work Much Better With Nouveau On Linux 4.5 where at least with Linux 4.5 it's fixed for Kepler.
While the Fermi/Kepler GPUs with the Nouveau NVC0 Gallium3D driver are up to OpenGL 4.1, the GTX 750 support is still limited to OpenGL 3.3.
Re-clocking isn't yet wired up correctly for the GTX 750 so the performance is still awful.
But a bigger problem than that is Nouveau constantly is spewing errors when running OpenGL test cases with the GTX 750...
So many errors in fact, the SSD got filled up. This isn't the first time this has happened with Nouveau, back from 2012: Nouveau Kepler Works, But May Fill Your Hard Drive.
Unfortunately when the SSD filled up, I also lost the slow OpenGL numbers that were recorded from the GTX 750 benchmarking on Linux 4.5 + Mesa 11.2-devel.
Long story short, the Nouveau open-source driver support isn't as baked nearly as well as GeForce 600/700 Kepler graphics cards. Hopefully NVIDIA will be able to step up their open-source support and help this year to the Nouveau drivers along with finally getting the GTX 900 series firmware out the door. At least though their proprietary driver continues working top-notch. I will have my Linux 4.5 Kepler results from this system published soon.