i honestly don't know the difference, other than you'll be able to change the wiring on the back, and you can't with the hi-amp. i have the same motor in a hi-amp, and i've asked what the difference is - other than the wiring options, and that the hi-amp is more expensive - and don't really know if one is more powerful (doubtful) or can handle higher amp loads.
regardless, you have one heck of a motor. it'll put a smile on your face, guaranteed.
are you pairing it with a MM? you should - they work great together. just get a fan to blow on the MM, and you'll be set.