The issue with microstepping is, it's essentially holding the motor's rotor in balance between two electromagnetic 'springs'.

I'd very much doubt even at high microsteppings settings, that the drives are actually translating that through to the output.
They certainly won't be as motor speed increases, as the drives simple won't be able to switch fast enough, and it'll gradually reduce microstepping. This is where digital drives provide benefits, and the higher spec drives (such as the EMs) dynamically change the switching points as they monitor how the motor is reacting.