As the owner of APU A8-3870K with Radeon HD 6550D I know, that performance of GPU isn't one of best, but should provide decent performance. This is what sometimes missing from open source implementation of graphic drivers. Situation changing these days and open source drivers being faster and faster.
Actual problem is, that with HyperZ functionality, which allows you use more potential of your drivers triggers some buggy code paths. I didn't noticed any for my Radeon HD 6550D, so I recommend enable it on this hardware. If you encounter some issue, please report it to bug tracker mentioned at bottom.
HOWTO: Before running game, set env R600_DEBUG=hyperz or pass it directly to game launcher.
After this step, you should get higher FPS in games.
NUMBERS: I did small benchmark on classic OpenGL. glmark2 2014.03 score: Without HyperZ: 515 With HyperZ: 717 With HyperZ 3.15 kernel: 741
Some additional information:
GL_RENDERER: Gallium 0.4 on AMD SUMO
GL_VERSION: 3.0 Mesa 10.3.0-devel (git-23e9f06)
Here is link to bug tracker. My proposal is white-list tested cards as yours or mine. If you agree, please let developers know your opinion.