What chip do you have in your Sharp? PXA250 or PXA255?
If you don't know, it's on the front of that lovely blue box it came in.
Basically, The Sharp Rom is slower, because it has some fixes for a bug in the PXA250 processor that they first shipped with. Later models used the PXA255, with no bug, but the same Rom, with the slower "fixed" kernel.
the OZ rom uses a special Kernel with no fix, which means it is unstable on a PXA250 processor, but fine with a PXA255.
If you have a 255, feel free to use OZ. With a 250, we kinda have to live with the speed, I have one too.
If you're really desperate, upgrade to a C3200. XD