How's the 14:1 worm reduction figure into this high speed machine? The worm gearbox slows down the driver, but cannot be back driven.
I do not know if Estop is ever "power braked" on a stepper system? The motor may coast. However, the moving load cannot effectively backdrive through a worm gearbox. Thus, the momentum of a heavy load could force the worm gear to try unsuccessfully to backdrive the worm, and it might bend or break something in the process.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)