I wouldn't worry too much about the distance from Burwood to Bankstown. I manage several in Canterbury/Bankstown LGAs and further west and I am on the North Shore.
You've hit the nail on the head but don't make your decision just on the $.
Who is the better PM? Will they negotiate for having 2 properties? (not a real big client but 50% better than one property).
Do they want to manage a solitary property in the area?