the only gain you get from 3" and 3 1/2" shells is more shot.They do not have anymore power in them than a 2 3/4" shell. which means the 2 3/4" shell will have better energy and distance and have more energy down range. The larger shells only have more pellets not any more powder. My slug gun I use 2 3/4 hornady SSTs. for turkey I do use 3" to have more pellets. Buck shot I use 2 3/4", may have a few less pellets but carry more energy when it gets there.
Born on a mountain raised in a cave huntin and fishin is all I crave