The open-source drivers always slaughter Lightsmark. Besides incorrect rendering, the performance is horrific. The Catalyst driver on the FirePro graphics cards is over ten times faster than Gallium3D.
The open-source Linux driver stack for Radeon graphics processors does work with FirePro graphics cards, but it does not really make much sense to use due to the much higher cost without any performance gain. As an example, the FirePro V8700, which sells for above $850 USD, cannot even handle running Nexuiz at a playable frame-rate with an HD resolution using the latest Gallium3D driver. You can find comparable or better open-source support out of a sub-$50 USD NVIDIA or AMD graphics cards. The performance remains crippled like the Radeon GPUs, the OpenGL support is still behind, and there are not any of the workstation features implemented in the open driver stack.
Those wishing to further analyze the test results or run a comparison can do so on OpenBenchmarking.org.