PS: Just for fun, have you seen this video: Here someone drives the VFD/spindle to its limit. It stays just below the VFD tripping. The video shows the ampères in the VFD display at the output (=spindle) side, and how their 220 V 2.5 kW spindle is driven to draw up to 10 A current from the output of the VFD (video): The test consists of driving a 10 mm 3-flute aluminium end mill through an 6061 aluminium block with 1000 mm/min feedrate, 10 mm depth of cut and 8 mm width of cut (for U.S. customary unit system users: A 13/32" 3-flute end mill through an 6061 aluminium block with 40 IPM, 13/32" DOC, 5/16" WOC).
Another test possibly could be to rough with a 8 mm roughing bit in black locust, one of the hardest woods in Northern America, 1/2" deep at 110 ipm, as shown here (they use a 6.6 kW HSD spindle on a Hitachi WJ200 VFD…)
By the way, on the first video where Piotr tests the 2.5 kW Jianken ATC spindle you can hear that the spindle is slowed down a bit on high load. Piotr uses a Huanyang HY VFD without vector control, so this slowing down is what vector control is trying to avoid. On the black locust / HSD spindle link, a Hitachi WJ200 (nearly identical to Omron MX2) is used that supports sensorless vector control, and you can clearly see and hear that is not slowed down despite the high load.