While there's at least another month left until the release of Mesa 9.3 / Mesa 10.0, for the mature Radeon R600 Gallium3D there are already a number of performance changes -- for both good and bad -- that can be spotted in running the latest code. Here's some benchmarks showing some of the performance changes over Mesa 9.2.1 stable for a Radeon HD 4000 series GPU on the open-source AMD Linux GPU driver.
As the next Mesa release nears there will be plenty more benchmarks across a wide-range of Radeon hardware -- like last month's 16-Way Open-Source Graphics Card Comparison that offered an early preview -- but for now to offer is an early Mesa 9.2.1 Git vs. Mesa 9.3-devel Git comparison with numbers from a Radeon HD 4870 "RV770" graphics card given its fairly common and popular status amongst open-source AMD Linux users.
Testing occurred from Ubuntu 13.10 with the Linux 3.11 kernel and xf86-video-ati 7.2.0 while comparing Mesa 9.2.1 and Mesa 9.3.0-devel from Git as of 8 October. The Mesa build was produced the same under both releases to look solely at the performance of the new Mesa code compared to what's considered stable at this point for the open-source OpenGL implementation. All benchmarks were carried out in a fully automated and reproducible manner using the open-source Phoronix Test Suite.