AMDGPU+RadeonSI Is Much Faster Than The Old Proprietary Fglrx Driver
The current performance of BioShock Infinite on the open-source driver stack is about doubled compared to where it was in 2014 with the fglrx proprietary driver.
The Counter-Strike: Global Offensive performance is largely the same while the newer R9 285 is 19% faster with the newest open-source driver code while the R9 Fury comes in at 15% faster.
Dota 2 with OpenGL rendering saw significant performance improvements with AMDGPU+RadeonSI, including a 60% rise in frame-rates on the R9 Fury.