The XScale in the Iyonix is crippled by a fault in the CPU's memory system meaning you can only access RAM at about 10% of the speed you should be able to.
Cortex-A8 in the Beagle board has a dual-issue pipeline which means that two integer instructions can be executed in parallel, as long as there are no hazards stopping this (e.g. one relying on the output of the next).
You also have the new VFP stuff that, given some supporting module, would give a great improvement in FP performance over the FPEmulator.
Finally, the OMAP chip in the Beagle also has a DSP which could be used to farm-off intensive codec-type functions, such as video decode, VoIP, etc.
Over all, I expect the Beagle board will significantly out perform and Iyonix in a number of areas.