Gray,
I've been fortunate enough to own and shoot the Xtrema I & II, and two of my hunting partners just bought the A400 Xtreme. I have shot the new A400 a few times out of the layout boat. If you are going from the Xtrema I to the A400 Xtreme BE CAREFUL!! Not because of quality, but because there is a difference in the length of pull!!
I still shoot an Xtrema I when I layout shoot, because I have orangutan arms and have a longer length of pull. Two years ago, I picked up an Xtrema II and the kick off is VERY NICE, but the LOP shortened up. I find that the A400 has a shorter LOP than the Xtrema II. If you need a longer length, you may be able to contact Beretta and see if they have a thicker recoil pad to give you the longer LOP. I have to say that the new Kick Off does seen to have less recoil, but again, I haven't shot it enough to know for sure. I do know that if I was shooting skeet in a T-shirt, I definitely would NOT shoot the A400 well because it is considerably shorter and changes my sight plane.
Best advice is to spend some time at the gun shop and shoulder the new A400. Also take your duck hunting jacket with you and shoulder the gun while wearing the coat. If it feels good, then go with it. You won't be disapointed with Beretta's quality!! The engineering with the new A400 is pretty damn cool!
Best,
Steve