The X850 has better drivers. Q3A is pretty old, so for the entire time the R300 era drivers have been under development it has been available for developers to optimise against.
It's really easy for 3D drivers to throw away most of the performance of the hardware in the name of keeping things simple. But until it works at all, simple is definitely the name of the game.
I'm torn on this. For every time I've thought "Wow, this is too slow, someone should really find out why" there's another time I've said "Damnit. The machine locked up again. Nobody should be optimising this until it actually works".
Manpower can't hurt though, and therefore funding to hire such manpower.