So the firmware won’t let you move faster than 300mm/s, that’s rapid or print speed. The stepper motors won’t move anywhere that fast as David states and as I have confirmed with experiments. 150mm/s is on the borderline and I have chosen not to go over 100mm/s. I don’t know what the practical speed limit of the extruded (print head) is. It might be a fun exercise to do a print test part that compares print speeds. The extruded speed is calculated for each move it makes to produce the thickness and width requested which will have to vary based on the speed it is moving. I personally have printed at 60mm/s. It would be nice to know the limits. “A man has got to know his limitations” (name that movie quote) 
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