Hey Brian,
I forgot to answer to this.
It may very well be that a spindle specified with 220 V / 8 A delivers a different amount of power (in kiloWatts) than another one that is also specified with 220 V / 8 A. You need to know that the values for voltage and current on the spindle nameplate are electrical values that occur during current consumption, but that the power specification “1.5 kW” or “2.2 kW” for a motor does not refer to the electrical power, but to the mechanical power at the end of the shaft.
According to IEC 60034-1, an electric motor shall be provided with a rating plate on which shall be marked the rated output. According to IEC 60034-1, the rated output is the mechanical power available at the shaft and shall be expressed in watts (W).
It is calculated this way.
So in this case it seems that the larger diameter of the rotor and stator on an 80 mm spindle already results in a higher leverage force acting on the axle than on a 65 mm spindle. Therefore, it may well be that the spindle delivers more mechanical power than a narrow spindle simply due to its size. In this case, it appears that this is the case with identical electrical current, i.e. for this 80 mm spindle you would not change the values for voltage and current in the VFD, but it has greater efficiency than the narrow spindle and delivers more mechanical power.
There are also some other parameters that can influence a spindle’s efficiency, like the amount, type and size of the bearings used (less friction), and others.