hmm, performance is allways relative to the kind of measurement you use. ..
Softfloat is one thing that can make some applications faster, but then running pocket workstation app in a chrooted environement you will not use softfloat.
Softfloat will make an application significantly faster if a lot of floating point operations are used.
For display, hardware graphics acceleration is another thing to take into account...I don't know if, on the 6000, there is a distribution that offers this besides the sharp rom. (pdaxrom does not) so X/qt might be "faster" on sharp rom than on OZ despite softfloat.
I think as OZ is able to run opie and gpe (X), not at the same time thus you don't have the 2 environements competing for resources, might be the best way to have the best of the 2 world.