But when I enabled Compiz, some other driver was installed and video performance is once again very acceptable. However, I'm not a big fan of the Compiz desktop effects. But switching off Compiz disables the accellerated video driver, for reasons I can not understand.
I remember the good old days when you could simply edit the xorg.conf to choose your driver. Now it's all dumbed down so Windows users don't get scared, and I'm stuck with effects I don't want to have. Gah.