I have never shot the 391, though I really want to, I owned 2 Benelli's but now just one. I love the reliability of a Benelli but they kick like no other. I am under 30 years old and the Benellis beat me half to death. I sold one because it was unpleasant to shoot. I think the reliability of the Benelli are idea for hunting, particularly waterfowl when a lot of heavy clothes will be worn. For trap I would definitely get a gas gun.
I can't offer any opinion on the two guns you asked about but I can tell you the Beretta Extema 2 has been my waterfowl gun until this season when I bought a Benelli Cordoba. I was apprehensive about the recoil shooting 3 inch duck and goose loads in the Cordoba but I can honestly say the Cordoba is a softer shooting gun for me than the Extrema 2.