We ran a S680 last year after running a 9770 that we still have and S670 that we traded.  Fuel consumption on the 680 is immediately noticeable.  The gauge looks the same at the end of the day but the tank is bigger.  Ran it two days pretty hard and emptied a 300 gallon transport tank.  Last year was a near perfect corn crop for us with high yielding corn on the majority of every farm so that wasn't too bad.  But before starting beans we had a 40' lined up to try to take advantage of the power and get gallons per acre down.  An 8 row in anything but 300 bushel corn would seem like a waste.