Approximate weight ratio between 50/60 Hz and 400 Hz electric machines
With motors, the rated torque is fairly closely related to the size/weight of the machine. The rated power is not so much related. A 400 Hz motor of a given size/weight will produce about the same torque as a comparable 50 Hz machine, but the rated speed will be eight times as fast. Since rated power is rated torque X rated speed X units of measure factor, the rated power will be multiplied by eight. That does not take into account some increase in losses due to increased speed and frequency.

In order to produce 8X power at the same torque and current, 8X voltage would be required. The core would support that magnetically, but the winding insulation would not. Higher voltage rated insulation might require some additional space.