Speedwise, some emulated applications may run slower on AROS since the emulation is a lot heavier. But native applications will run a lot faster because the x86 will be a lot faster than PPC (at least today's x86 are faster than the fastest PPC OS4/MorphOS run on: who knows ? This may change in the future 
).
True, ARM may be joining x86_64 being the faster then PPC in the near future
