Radeon Gardenshed DRM + Gallium3D Benchmarks
At 1920 x 1080, OpenArena is on the brink of not being playable for the tested hardware under Gallium3D + Gardenshed DRM.
Obviously, at 2560 x 1600 the performance is even worse. Those running such 30-inch displays will tend to want to stick to the proprietary drivers anyhow.
The Catalyst driver on the Radeon HD 4000/5000 series hardware is still many times faster than the open-source code.