Longtime lurker here, first post - thought I could contribute to this one . . .
I own both an A400 and a Super Vinci (long story as to why), but here goes . . .
First, the A400: Beretta sem-autos have never fit me well, although the latest A400 wasn't too bad. The recoil was minimal, the bolt operated quickly, and I liked the gun. That being said, I continue to have a lot of cycling issues with all but the stoutest of shells, and cleaning the thing is a real pain. Not as bad as cleaning a 391, but still pretty bad.
Now, the Benelli: Yes it looks a little unusual, but it handles and points very nicely. I find myself reaching for this gun for more than just waterfowl hunting (which was all I ever thought I would use it for). I suppose there is more felt recoil than with the A400 with similar shells, but unless I'm shooting 3.5" shells (which is rare - geese only), the recoil doesn't bother me. the bolt operates kind of slowly, which took a bit of getting used to. It has been absolutely bombproof, and easy to clean. The other day, I shot sporting clays with it, and used 1 oz. Winchester AA target loads, and it cycled perfectly. It is also, thanks to the funky design, a breeze to clean.
Between the two, I find myself reaching for the Benelli much more often, and always for duck hunting, but if I was going to go to the clay range and shoot a high volume of targets, I'd probably opt for the heavier A400.
Edit: I picked the Super Vinci over the regular Vinci for 3.5" capacity, and because everyone was saying that the trigger guard on the Vinci would jam their finger, and that Benelli fixed this with the larger guard on the Super Vinci. Since then, I've shot a regular Vinci, and didn't notice any issues witht he trigger guard. Given how rarely I shoot 3.5" shells, if I had it to do over again, I might have gone with the regular Vinci just to save a few bucks.