> What would you think creates these inefficiency issues?

Good question. But I've to admit that I really don't know. Freescale presented the e5500 as being basically a 64 bit capable version of the e500mc (hence the 'e500mc64' moniker) with an enhanced FPU (but which of course is irrelevant in terms of integer performance). With that said it's really strange that in terms of DMIPS the e5500 is 24% less efficient than the e500mc.