Phoronix reports the state of open-source Linux graphics drivers for AMD's Radeon graphics cards is improving. The proprietary AMD driver is still better, but in some cases the open-source Radeon Gallium 3D driver now outruns Catalyst. Full details at Phoronix.
"In this article are benchmarks of the past two Ubuntu Long-Term Support releases (Ubuntu 12.04.1 LTS and Ubuntu 10.04.4 LTS) compared to the latest Ubuntu 13.04 development state. Being looked at specifically for this round of testing is the AMD Radeon Linux graphics performance with the latest open-source driver compared to an older Catalyst driver. For an AMD Radeon HD 4800 series graphics card, the current state of the open-source graphics driver on Linux is beginning to outperform an old AMD Catalyst driver from 2010 for select Linux OpenGL games."