Phoronix published a review on the 6-Way Ubuntu 14.10 Radeon Gallium3D vs. Catalyst Driver Comparison
A quote from the article:
As a follow-up to last week's Ubuntu 14.04 vs. Ubuntu 14.10 AMD Performance Comparison and yesterday's Radeon R9 290: Gallium3D vs. Catalyst driver comparison, here's taking things further in looking at the performance of the open-source AMD Radeon Linux graphics driver in several configurations while compared against the closed-source AMD Catalyst graphics driver as found on Ubuntu 14.10.6-Way Ubuntu 14.10 Radeon Gallium3D vs. Catalyst Driver Comparison @ Phoronix