With the very lax OpenArena game the Radeon HD 5830 and Radeon HD 6870 performance exceeds the Catalyst driver. The Radeon HD 4870 and Radeon HD 6950 graphics cards also experienced performance boosts in the newer Mesa and Linux kernel.
With the slightly more demanding OpenArena 0.8.8, the R600 Gallium3D performance was behind the Catalyst driver but at least over 50% the speed of this binary blob. The performance for the Radeon HD 6000 series graphics cards seemed to improve with the Linux 3.13 kernel.
World of Padman was a similar story to OpenArena. In terms of why no Source Engine / Steam games were tested, read about Running Benchmarks On Other New Linux Games.