Mesa 13.0 vs. 17.0 vs. 17.1 Git RadeonSI Tests
Mesa 17.1-devel didn't show any gains for Deus Ex: MD with the higher quality visuals.
Dota 2 with its OpenGL renderer was faster with each consecutive Mesa update.
ET: Legacy has even experienced some performance improvements with the Mesa updates.
The Radeon R9 285 was benefiting from Mesa 17.1-dev while the RX 480 and R9 Fury didn't see much in the way of performance changes.