Hi,
You might glean some info by putting an oscilloscope across a current shunt resistor in the servo power supply lead, to see what peak and instantaneous currents you get.
It will be interesting because those cheap servos are not exactly consistent in performance.
I have quite a few here and even checking the spindle backlash can be noticeably different from one unit to the next.
I just bought a pack of 10 of the sg90 on abay for a ridiculous low price to use and abuse for some projects for my brother's N Scale layout.
Tom.... 