Stepping up 240V to 480 or 600V, running 900 feet, and then stepping down to 240V strikes me as a very bad idea.
What you save on voltage drop in the conductors, you lose on the impedance of the two additional transformers in the circuit. Say you size the transformers right to load, and they each have a 2.5% impedance. This would be a 5% voltage drop without even considering the voltage drop in the service (feeder) conductors. Once you factor in the losses associated with oversizing the transformers, and the cost of the transformers, simply running fat conductors starts looking much more attractive.
Unless I totally misunderstand transformer impedance (won't be the first time).
Seems to me that the 'right' way to do this is to bring the primary distribution voltage underground onto the property, and place the transformer near the house as Bob (not iwire, who is also a Bob) suggests. Not taking 240V and stepping up to 7200V, but simply starting with whatever the local distribution voltage is, and stepping that down to 240V near the point of load.
Or simply design for the start for the voltage drop, eg. dividing loads up onto separate feeders, one with large allowed voltage drop, one with small allowed voltage drop.
-Jon
