Quad-Monitor AMD/NVIDIA Linux Gaming: What You Need To Know
Starting off with Doom 3, for this old game -- but representative of other modern games like those using the enhanced ioquake3 engine or other non-GPU-demanding titles -- it is possible with the GeForce 700 series or a Radeon R9 290 to handle the 3840 x 2160 OpenGL workload at a very playable frame-rate across four 1080p displays when using binary AMD/NVIDIA drivers. The GeForce GTX 780 Ti and TITAN obviously ran the best. The Radeon HD 6950 with the open-source R600 Gallium3D driver struggled and put out an average of only 42 FPS.
The Prey results aren't too different from the Doom 3 results given that they're running on the same engine, but worth pointing out here is the Radeon R9 290 issue. The R9 290 is still troubled by a buggy Catalyst Linux graphics driver and for Prey it happened to barely be running faster than the Radeon HD 6950 on the open-source driver.
Unigine Heaven results weren't available for the AMD hardware due to the R600 Gallium3D driver not yet supporting Unigine Heaven 4.0 (for the HD 6950 on the open-source driver) and the Radeon R9 290 had the aforementioned full-screen issue with the newer Unigine tech demos. When it came to running Unigine Heaven at 3840 x 2160, the NVIDIA GK110 GPUs could only put out 18 frames per second.