Phoronix published a review on the Windows 10 vs. Ubuntu 16.04 Graphics Performance With Radeon Software, AMDGPU-PRO, AMDGPU+RadeonSI

A quote from the article:

Yesterday I published some Windows 10 vs. Ubuntu 16.04 Linux gaming benchmarks using the GeForce GTX 1070 and GTX 1080 graphics cards. Those numbers were interesting with the NVIDIA proprietary driver but for benchmarking this weekend are Windows 10 results with Radeon Software compared to Ubuntu 16.04 running the new AMDGPU-PRO hybrid driver as well as the latest Git code for a pure open-source driver stack.

Under Windows 10 Pro x64, the Radeon Software Crimson Edition 16.6.1 driver was used for benchmarking. Under an updated Ubuntu 16.04 stack, tested first was the AMDGPU-PRO Beta 2 (16.20.3) driver. After testing this hybrid driver, the Linux 4.7 Git kernel was installed along with Mesa 12.1-dev and LLVM 3.9 SVN via the Padoka PPA for providing a very bleeding-edge look at the open-source AMD/Radeon Linux graphics driver performance.

 Windows 10 vs. Ubuntu 16.04 Graphics Performance With Radeon Software, AMDGPU-PRO, AMDGPU+RadeonSI @ Phoronix