If you are looking at motor specs, use the 5/8″ orifice to compare the motors actual cleaning power. This opening best illustrates the cleaning performance that you will have when cleaning.  The  5/8″ (0.625) opening is the size of the opening on a cleaning tool.
We have all our motor specification sheets on our website so that you can get an accurately compare the motors.  Many times you will see the airwatts based on peak or maximized airwatts which is calculated by using the maximum voltage.