Either isvery good choices. Both models have some improvements over their first models. The SBE II has bigger trigger gaurd and a better action/recoil spring assembly. It should drain better and be quite a bit easier to take apart. The Xtrema II is a tad bit lighter even though it's listed the same as the Xtrema. The forearm has deeper grooves which makes it feel a little thinner. The stock is also thinner in the wrist area. It still has that wide grip.
I'mnot sure how much the KickOff system on the Beretta works as I have not shot the Xtrema II. I have shot the SBE II next to a SBE with various loads.The ComforTech does not offer any reduction in felt recoil. The removeable comb is soft and could help some with face slap. Thereis a taller one that can be inserted. It's a nice feature and the next best thingto an adjustable one.
Both guns have automatic magazine cutoff's. The Beretta has a bolt lock back lever that the SBE II does not. Both come with shims to adjust to stock for drop and cast. They have a similar balance with more weight towards the stock. The SBE II is a little lighter. The Xtrema will more than likely cycle lighter shells better. The Xtrema II is easy to clean with the SBE II being even easier. If you include cleaning the action/recoil spring and tube the Xtrema will be easier. The Beretta holds five shells to the SBE II's four (Non waterfowling).You need to hold each to see which you like the best. I would suggest to also look at the Browning Gold 3 1/2" model it's equally good.