Not that much of a difference in velocity. This is a personal preference, but on a pump or autoloader a 24-26" barrel is a good compromise. I generally use 26" for everything, including waterfowl. Longer barrels help with a smoother swing much more than velocity. For a pure waterfowl gun a longer barrel would help a bit on longer passing shots. Not because of velocity, but balence, a smoother swing and longer sighting plane.
The shorter 22"-24" guns are quick pointing for grouse or quail where birds are fying straight away, but give up something on passing shots To me the 26" is just the perfect all around length on a repeater. On a double, because of the short receiver a 28" gun gives about the same balance and overall length.