It would be interesting to see the Dhrystone benchmark for 5600s with the PXA255 that still have the original ROM that they were shipped with. I have a feeling they are being shipped with the crippled kernel.
Get the Dhrystone binary here:
http://laurent.lieben.free.fr/zaurus_kernel/dhry21Copy it to your Z, make sure it is executable and run it with 50,000,000 iterations (may take a couple of minutes) and then post the contents of the file dhry.res that is created in the current directory.
A 5600 with a PXA255 should get something like the following if it is running at full speed:
Microseconds for one loop: 2.5 (The lower the better)
Dhrystones per second: 400.0 (The higher the better)
VAX MIPS rating: 230 (The higher the better)