"As far as why the open-source driver is outperforming the highly optimized closed-source driver, Stefan wrote, "I don't have an explanation for this yet, especially considering that fglrx beats r600g by a factor of 5 in most of your Linux-native tests. A possible cause is that my test setup is heavily CPU limited (usually 800x600 resolution, no multisampling). This was a conscious decision when I set up the tests because Wine's main performance issues are on the CPU side, not the GPU side. However, at least r300g's main problems seem to be GPU-related (not sure about r600g).""
Unless he means, WINE has CPU issues when using AMD drivers, I disagree. WINE had no CPU bottlenecks in all games I played (NOLF2 and stuff).
Still, even with 800x600 this shows open driver has no resolution-associated CPU issues, which is good.
Running 1920 parallel would be good though, even if opensource looses.
I think he might be refereing to that Wine it self dosn't do a lot in GPU space so optimizations are focused on CPU and there for his test is also set to mainly stress CPU bound functions.