If I remember correctly some of the improvement to the 14xx series when they when to the 16xx series was larger elevators, both clean grain and return and improved capacity for handling wet corn and rice. Rotor cage was changed too. Early Cummins engines used on the 16xx series were run at 2600 rpm and caused some problems, but I think that was resolved. So maybe the 1680 would be worth the extra money in your situation. A 1688 would be a better choice.