Hey Dave,
the motor current setting in the VFD (here: F142) has to be set according to the rated spindle current in spindle manual or nameplate.
See → here for details (and also here).
You also need rated voltage and number of magnetic poles.
If you want to see more Ampères flowing you can do this test to drive your spindle to its limits 
this is the spindle limit that you may confidently exploit but whether this is good for the bit or the cut depends on what is appropriate for the result. What matters is the speed of the cutting edge and whether you have good chips (on wood milling, what matters is to evacuate heat, therefore rather high speeds, and it’s the chips that evacuate the heat), I would start with relying on bit manufacturer’s recommendations for the bit, and then try it out.