The problem is that you cant do a direct 1 to 1 comparison between the open drivers and fglrx. The open drivers dont have the same level of functionality yet. And with fglrx more than half of the "supported" functionality is so buggy that it isnt at all usable. Even though 2d support isnt fully implemented it still outperforms fglrx. Even though video decoding isnt at all supported it still outperforms fglrx. Even though modesetting is still a bit buggy, dual monitors at least work with the open drivers and are completely impossible due to massive show stopping bugs in fglrx.
As far as the truth is concerned the only performance advantage that fglrx has over the open driver is 3d support. Most of that advantage will disappear once OpenGL3 comes along... and what little advantage it gets from tuning will be completely worthless considering the open driver actually works and fglrx doesnt.
So I guess the question is simply this............
What would ATi do if the open driver comes out on top and outperforms fglrx in 3d tasks, just like it does now on everything else?