Download AROS for free and enjoy it for what it is. Mind you, all your classic Amiga experiences will have to be emulated, and I can assure you that UAE is no where near as fast as Amithlon, especially when it comes to the non WinUAE variants. So basically you will find your self not running classic Amiga software so much as you will be running new software written/ported over for AROS use.
I LOVE AROS, but it's not in the same league as MorphOS which actually allows you to run a large sum of the classic library without the need of emulation. Likewise MorphOS is so far advanced at this point that it is going to take all other Amiga clones a while to catch up with it and by that time MorphOS will be more advanced still!!!
Well the x86 CPU speed is faster and cheaper than Apple G4 PPC hardware. I can't see it being slow on a peanuts $99 AMD Athlon XP3900+ box surely?