RE: 3 or 3 1/2???
I like the 3 1/2" chamber for waterfowling. The real advantage is when shooting steel loads. When shooting steel, speed is an advantage. A 3" shell in steel at 1,550fps has only 1 1/8oz of shot. A 3 1/2" shell in steel at 1,550fps has 1 3/8oz of shot. Pellet count for #2 steel is 140 for 1 1/8oz and 171 in 1 3/8oz. In extrema cold shells can loose velocity as well.
One other advantage is if you run out of shells in the blind. If all of your buddies are shooting 3 1/2" shells and you only have a 3" gun, you're out of business. I don't NEED a 3 1/2" gun just like I don't need a car that is faster than 70mph either.