The question is always "What is the next most valuable pound of weight and dollar of cost going to buy that makes the aircraft safer?" Example: should we spend 100 lbs (invented number) going from SS5 to SS6 on the floats, or provide 100 more horsepower when OEI? Both weigh 100 lbs, which makes the aircraft safer? Which do we burden the aircraft with?
Nick thanks for the insightful and (at least for me) illuminating information on the engineering considerations - well put.