Phoronix published a review on the Radeon Gallium3D Is Running Increasingly Well Against AMD's Catalyst Driver A quote from the article:

After last week running new Nouveau vs. NVIDIA proprietary Linux graphics benchmarks, here's the results when putting AMD's hardware on the test bench and running both their latest open and closed-source drivers. Up today are the results of using the latest Radeon Gallium3D graphics code and Linux kernel against the latest beta of the binary-only Catalyst driver.

Similar to the NVIDIA GeForce tests of last week, on the open-source side was the Linux 3.16 kernel with Mesa 10.3-devel and other updated graphics user-space using the Oibaf PPA on Ubuntu 14.04 LTS x86_64. When benchmarking the proprietary Catalyst 14.6 Beta driver from mid-July, we had to pull back to the Linux 3.14 kernel for kernel compatibility with this binary blob release.

 Radeon Gallium3D Is Running Increasingly Well Against AMD's Catalyst Driver @ Phoronix