AMD & NVIDIA: Open vs. Closed-Source Driver Performance
As very little surprise given the maturity of the open-source AMD driver stack and AMD's investments into that driver, right away with Counter-Strike: Global Offensive we see the open-source driver meeting or exceeding the performance of their AMDGPU-PRO hybrid / closed-source driver. Meanwhile the Maxwell cards on Nouveau are unplayable due to no re-clocking support and then for the Kepler cards they are still not up to compete with NVIDIA's proprietary driver.
With Dota 2, AMD's open-source driver performance is the same for the RX 480 and superior on both the R9 285 and R9 Fury.
Under the ET: Legacy game, the open-source drivers lag behind the closed-source drivers across the board from both vendors.