I think I understood that.
I apologise if this is a stupid question but could I supply 12v to the arduino barrel connector and take the servo power from the VIN pin through a 7805 and diode as you suggested?
In fact considering the rating of the servo is 4.8v - 7.2v would a 7806 and no diode be better?
I just want to keep things are straight forward as possible and a 12v power brick should be easy to find.