Hey Echd,
probably rather low 
But I think that is the situation of hundreds of users who bought a VFD that in fact is rated and perfectly able to draw too much current from their supply circuit, but do never become aware of this fact, because 1. the maximum VFD input rating is willingly omitted by the cheap chinese manufacturer both in the manual and on the nameplate, and 2. they never run the spindle in a load range where it could come close to the limits. When I look at the projects in “Post up them projects”, I can imagine that many projects probably don’t really demand the milling motor.
That’s what the cheap chinese VFD manufacturers hope for, that no one will find out what the input rating specification should have been on those 110 V 2.2+ kW kits – and what the serious manufacturers avoid, by producing either no 100 V class VFDs at all, or only up to 0.75 kW like Hitachi does.
But did you have a look at the test I described above / video I mentioned above? It’s not that difficult to drive the VFD to the limit by mechanical load, if you really want to. I think it is useful for anybody to have a feeling of how far this limit is.