Current through the coil is proportional to the time that the voltage has been applied, and inversely proportional to the inductance:
I=V⋅TL
Time is given by:
T=I⋅LV
For one step, the current must go from 0 to Imax and back to 0, or alternatively from −Imax to +Imax:
I=2⋅Imax
The time for a single step is:
T=L⋅Imax⋅2V
To compute maximum revolutions per second, divide seconds per step by steps per revolution:
Rev/sec=VL⋅2⋅Imax÷stepsrev
Maximum power is given by:
Pmax=2⋅Imax⋅V