As some recent non-performance testing of the AMD and NVIDIA graphics drivers on Linux, I checked in to see how well the various Linux desktop environments were working these days in multi-monitor setups. With the latest AMD Radeon and NVIDIA GeForce graphics cards and drivers, I tried out Unity, GNOME Shell, Xfce, and (attempted) KDE Plasma 5 on Ubuntu 15.04 to check out the latest experience.
Back in 2013 I did the quad-monitor AMD/NVIDIA Linux gaming comparison which provided interesting numbers for the time, but with doing 4K tests these days now that the Ultra HD monitors are more common, this weekend's testing just focused on the desktop experience when driving four 1920 x 1080 displays with the different desktop environments on Ubuntu 15.04.
To no surprise, using the NVIDIA binary graphics driver led to the best experience... The NVIDIA binary blob has been supporting modern versions of the RandR extension for some time now and the nvidia-settings control panel offers arguably the most multi-monitor display configuration options. From the NVIDIA X Server Settings panel allows easily altering the monitor layout, changing the orientation, and altering various options like underscan.
The NVIDIA panel applies these settings in real-time while there's also the option of saving the display configuration options out to the xorg.conf for making it more persistent. This interface to NVIDIA's binary blob is very easy to use yet very feature-rich. With supporting modern RandR, you can also use any of the other Linux desktop monitor configurations too if you prefer using your own desktop's utility instead.
While nvidia-settings doesn't integrate as well with the different desktop environments as do each desktop's own utilities, nvidia-settings is very advanced and offers everything one should need. Testing of the NVIDIA hardware with the Nouveau driver wasn't done since the modern NVIDIA GPUs on Nouveau still run into re-clocking issues and driving multiple 1080p displays while the GPU -- and especially the video memory with needing to scan out multiple high resolution displays -- are running at very low speeds would be a problematic experience.