I've had two 3.5" chambered shotguns. A Mossberg 835 and a Benelli Super Nova. My brother has a 3.5" 870.

Sold both of mine and went back to a 3" 870. My brother still owns his POS.

With the hundreds of non-toxic loads on the market nowdays,a 3" chamber will do everything you need to do with a 12ga.

If you think you need a 3.5" 12ga,you'd be better off with a 10ga IMO.