I'm currently budget shopping for a Class A Pusher, 40 plus feet, tag, and preferable a Spartan. I live in the northeast but will be making regular trips to bay area in California, and Phoenix AZ. We are very comfortable with the coach models that offer 450hp, and although they are nice don't really need the extras that the 600hp models offer. However I don't want to be disappointed climbing the mountains going to California, especially pulling a Mustang in a car trailer. Is there also a mileage advantage with 600hp?