We just inherited a Professional 6 model (the one with the two flanges on the side that uses a handle to lift it into position). We have the less expensive "Legendary Stand Mixer". The first thing we noticed is that the motor of the larger machine not only is air-cooled, but there is a whine that the motor has which the other one does not. If this whine is related to the air cooling, that would make sense, but if not, then we will try to find someone to refurbish it.
We would be grateful if someone who has the Professional 6 model could chime in...