I would expect those steppers, even on 24v, to handle 2000 full steps/sec easily, thats 10rps, 600rpm or 1800mm/min with little load...

80mm/min = 26rpm = 0.43rps, 86 full steps/sec

have you told MACH3 you are using 1/8 step?

It does suggest your MACH3 settings are wrong...