2016 End-of-Year Open-Source Radeon Benchmarks With Linux 4.9, Mesa 13.1-dev On Many Different GPUs
Dota 2 7.00 was working with RadeonSI and R600g all the way back to the Radeon HD 4890! But here at 1080p, the HD 4890 and FirePro V8750 were delivering below a 30 FPS average... The Radeon R7 260X and above were above a 60 FPS average for this fully open-source AMD Linux driver stack.
3840 x 2160 is rather tough for the older hardware, but these 4K tests were done primarily to stress the newer graphics cards that otherwise aren't really busy with 1080p workloads. The R9 Fury was the only card on the open AMD driver stack to run Dota 2 7.00 at above 60 FPS.
ET: Legacy is the open-source Wolfenstein Enemy Territory re-make that's ongoing with an OpenGL 3 renderer and many engine improvements while slowly also re-creating all of the art assets as free. Given the age of the original game, to no surprise it runs on all of the old GPUs tested and continues scaling up through the newest cards thanks to its GL3 engine rewrite.
Similarly, the OpenArena ioquake3 game results for those interested in this open-source game and how AMD's performance has evolved since the RV770 days.