Well, given our frequent OpenGL and Vulkan benchmarks, these results were a pleasant surprise to see... Darktable OpenCL works particularly well with AMDGPU-PRO and overall performs better than NVIDIA's proprietary driver. It seems the NVIDIA Linux driver might have some issues given the oddity of e.g. the performance between the GTX 980 and GTX 980 Ti being rather extreme and some of the Maxwell cards performing outright slow. The GTX 1070 and GTX 1080 were running out in front.
The NVIDIA Pascal results aside from the GTX 1050 series fortunately don't appear to be affected by any Linux driver problems with delivering stellar performance, but again with these scenes the AMDGPU-PRO OpenCL results remain rather exciting. But keep in mind this is with AMDGPU-PRO as the open-source OpenCL stack isn't yet good enough until it goes through the ROCm overhaul.