This has been asked here about a year ago. I would rather have a denser shot pattern than the small amount of additional sped you are talking about considering most ducks don't exceed 60 mph and none of them approach the speed of the shot in either shell you are asking about. 1450 fps equals 988 and change mph and 1550 equals 1,056 and change mph. We are talking about shooting down ducks here, not jet fighters, 78 mph really is not going to make a difference between the two shells. As long as you do your part and shoot them where they eat and not where they crap you will kill them. I use 2 3/4 inch Bismuth shells ever since they hit the market. I never really saw the need to use 3 or 3 1/2 inch shells for waterfowl since I do not shoot at them in the stratosphere, I shoot over decoys.