Personal preference regards Drives/PSU doesn't really come into it regards speed.? . . Speed should not be thought about has been got from drives or motors but from the correct choice of screw pitch. Yes to get best performance from motors then voltage and therefore drives/PSU play a part but it's the screws and the relation ship with running motors in the right RPM range in conjunction with machine size and intended purpose or goals that make the difference between getting it right or wrong.
Cutting corners regards drive quality or PSU size is THE most common mistake new CNC'rs make.!! . .. . . unfortunately it's mostly after weeks or months head banging they find out.!
see there is me misunderstanding the reason behind different sized motors. however when it comes down to running the motors in the right RPM range, is it really a case of buying the right motor if you got it wrong or can you make the wrong motor work for you if you are using belts and pulleys?