400 Hz

Incidentally, a way to get three phase power at a frequency of your choice is to use a "variable frequency drive". That's basically a high power solid state inverter intended to drive three-phase motors with a chosen frequency resulting in the RPM of your choice. Depending on the model, those can go up to 120 Hz or so, or all the way to somewhere around 400 Hz. I have a very cheap one at home that runs on single phase 220 volt power, producing up to 3 kW or so at anywhere up to 120 Hz. (Made by a company named Teco, amusingly.) Most of these and especially the larger ones want three phase mains input, though I'm told that even for those you can typically just connect them to single phase power (between two of the three inputs, leaving the third unconnected) at reduced power ratings. These devices are surprisingly cheap, in particular they tend to be cheaper than "rotary phase converters" which is how machine shops traditionally produce three phase power when their mains is just single phase.