LambdaFF is right.

The limitating factor is NOT how fast you can move your steppers, but how fast you can melt and squeeze the plastic out of the nozzle. Melting takes time, and the faster you go the more friction you get and the more pressure you build up before the nozzle (to the point the hardware fails, bowden tubes springing loose, hobbed wheels grinding etc).

Increasing stepper speed may optimize the total printing time a little bit, increasing extrusion speed will do much and much more. At this point of technology, the extruder is the limiting factor, not the steppers.