When starting out with the Nexuiz title and running it at a resolution of 1024 x 768, the Catalyst 10.10 driver was many times faster than both the classic Mesa and Gallium3D drivers. The Gallium3D driver on ATI Radeon HD 5000 series was not even working for us with this open-source game. With the Radeon HD 4870 graphics card, switching to the Gallium3D driver over the classic driver resulted in a 15% jump in frame-rate performance. These frame-rate levels were only just playable even at this low resolution while the proprietary Catalyst driver was 4.5x faster.
When increasing the Nexuiz resolution to 1920 x 1080, the performance with the Radeon HD 4870 that is still considered relatively powerful by today's standards was not at a playable frame-rate to any gamer using either open-source driver.
With the VDrift open-source racing game, the classic R600 Mesa driver couldn't even run. With the Gallium3D driver on the Radeon HD 5000 series, like Nexuiz, resulted in the game not getting beyond the loading screen. Fortunately, however, the Gallium3D driver paired with the Radeon HD 4870 worked out well. To some surprise, the Gallium3D driver actually ran at 50% the frame-rate of Catalyst. Still this puts the Gallium3D driver as still barely being playable for this somewhat-demanding game, but compared to the Catalyst driver this is some of the best performance we have seen out of an open-source driver.