Phoronix published a review on the AMD Radeon Gallium3D Is Catching Up & Sometimes Beating Catalyst On Linux A quote from the article:

Last week I posted the original 16-way CS:GO and TF2 Radeon Gallium3D results while today's numbers have the Catalyst result added in using the fglrx packaged driver for Ubuntu 14.10. As mentioned in the earlier article, Team Fortress 2 and Counter-Strike: Global Offensive were chosen as being two popular Steam on Linux games with CS:GO having only been released a brief time ago for Linux. Both games also meet our requirements for automation and interaction with the Phoronix Test Suite for fully automated and reproducible performance benchmarking.

 AMD Radeon Gallium3D Is Catching Up & Sometimes Beating Catalyst On Linux @ Phoronix