3.5" are slower in velocity than a 3", they just throw more shot. VELOCITY KILLS not amount of shot you are chunking out there. I shoot reloads through my Benelli M1 and kill geese and ducks from close range to 50 yards. 3.5" are good for turkey's but not much else.
Buy what feels right....I have had no trouble with my Benelli. If I were to buy again, it would be a SBE II or Beretta. I just like Italian guns. The other guns mentioned on this link are also quality. I would buy about anything but a Browning Gold. I have a buddy that has had mucho trouble with his and it is jap made.
Why a 3.5 12 ga? If I were in need of that much firepower, I'd get a 10 ga. The guns are heavier and absorb recoil better and you get a shorter shot string and tighter patterns. Personally 3in Heavi Shot kills anything legal to shoot at here. We don't have a Swan season yet.
I am not as much of a fan of the SBE2 as I am a fan of the M-2 or M1. They cycle faster than the SBE2, because they dont have the 3 1/2 inch chamber. I traded my m1 for and sbe and then traded it back in for another M1. Its a great waterfowl gun.