Good question, no good answer, I don't know what I want...

High speed may be preferable to high power?
Cool running is nice.
A sexy power against speed graph that doesn't fall of a cliff could get my juices flowing.
Something that doesn't come in sets of 3 is handy because X and Z can be very different.
I do know it will drive a 4mm ball screw using timing pulleys, I have a thing about XL pulleys