Be sure to watch your temps on 6s. You will actually be increasing the wattage being put out by the motor therefore increasing the heat it's putting out (it's not 100% efficient, afterall). If you can swing the cash, I'd go with 4s and 6s so you can have insane power when you want it but you can also tame it down to a more reasonable level.
All I ever wanted was an honest weeks pay for an honest days work.