When running Nexuiz at 2560 x 1600, the Radeon HD 6870 was running at 120 FPS for this game, which is one of the most demanding open-source first person shooters available. However, even a Radeon HD 5750 graphics card is more than enough for a playable experience with this game when using the Catalyst driver.
With Xonotic, the forked Nexuiz game that's currently in development, the spread between the Radeon HD 6870 and the Radeon HD 4870 X2 / Radeon HD 4890 graphics cards was even greater. Unfortunately, with these results there are no Linux benchmarks for the Radeon HD 5870, Radeon HD 6850, Radeon HD 6900 series, or similar ASICs, including competing GPUs on the NVIDiA side, due to not having access to such graphics cards at this time.
The frame-rates in Lightsmark are always high when using the proprietary NVIDIA / AMD drivers and with the Radeon HD 6870 they were well in front of the other five graphics cards that were benchmarked for this Sapphire Linux review.