Something else to consider for Voltage Drop calculations:
How 'steady' will the voltage drop be. If the lights run a little bit dimmer when every thing in the house is on, than that probably is acceptable.
But if every light in the house gets substantially dimmer for a moment whenever the well pump cycles or the heat pump turns on, than that might not be acceptable to the homeowner. Even worse if the voltage dip is enough to cause electronics to reset!
I would strongly suggest finding the load with the largest inrush or startup current, and checking the voltage drop when that load starts up. If you run the bare minimum 2/0 wire for a 200A service, you might easily get >10% momentary voltage drop if there is a large motor load on the property.
Another thing to consider: given the length of the underground run, would the POCO place a padmount transformer near the home, with most of the underground run at distribution voltage?
-Jon
