Barrel length after about 20 inches is really only going to improve your patterns with turkey loads and maybe htl waterfowl loads. It won't do much for velocity as most of that is gained in about the first 18-20" or so of a shotgun barrel. What it WILL give you is a longer sight plane, more weight up front to help with swing through and generally a bit less recoil, again due to the added weight. I use a Benelli SBE II with a 24 barrel and it flat SHOOTS. I do use extended chokes for turkey and waterfowl, giving it about an extra inch or two at the muzzle. The big thing with short barrels is if you hunt with other folks, especially in pits or layouts where you're close together...
MAKE SURE YOU STAY IN YOUR SHOOTING LANE!!! While you can ring some ears with any length barrel, the muzzle blast from a short one swung too far to the left or right might just get some empties thrown at you...or something heavier. Also, is your barrel ported? I assume it is if it is a newer model. That is another thing to worry about. The porting will ring the guys ears sitting next to you far worse than the short barrel. The 935s are seriously good shooting guns and can out pattern guns costing many times as much. As far as the rear sight, (is this the turkey model?), I would just take it off if you are going to use it for waterfowl. You'll just have to pattern it and find the best load and choke for whatever application you use it for.

Oh yeah...welcome to the site!

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Try shootin em in the rooter, not the tooter...