The 3 1/2s were developed for the steel shot loads for ducks and geese...to give denser patterns....Will you be decoying birds or pass shooting??? Also, with the development of tungston, heavy shot etc....Do you still need the added recoil of a 3 1/2??? Is the 3 1/2 heavier than the 3 inch??? Do you want to carry the extra weight and how does it affect the balance...
For turkeys, a 3 1/2 is just is not needed...My dad was a market hunter back in the 30s...He killed more turkeys than most of us will ever see...He used a 12 gauge, single shot, 2 3/4 inch full choke wiith Remington #4s...
I have a Browning B-80 that puts about 15 pellets into a turkey's head and neck at 40 yards, using Federal Premium #5s...I see no need for any more.. Down South, 40 yards in the Spring turkey woods is a long ways...If I can't get them closer than that, I just get more hunting time in!!!
Another thing...a 3 1/2 with a turkey load has a good kick to it, especially in a pump...Flinching is a terrible habit to try to cure...I have seen more deer wounded by flinching than any other reason...
Guess I don't think a 3 1/2 is needed...In fact, I would go with a 10 gauge over a 12 in 3 1/2 because of the shorter shot column...