RadeonSI OpenGL Performance Has Evolved A Lot Since Early 2015
Tesseract saw less of a performance boost on the open-source Radeon driver over the past year and a half, but still it's up by 20%.
The Xonotic results were mixed with Ubuntu 15.10 but going from Ubuntu 15.04 to today the Radeon R9 270X is faster by about 20%.
Furmark sees some modest performance boosts over time too.