Shot SIZE is not relevant to velocity, therefore distance. Shot WEIGHT is going to determine distance with a given powder charge. ie if you are using a 3 dram equivalent with a 1 1/8 oz shot charge, it doesnt matter if the shot size you are shooting is #9 or #3. The powder charge is pushing a WEIGHT, the size of the individual shot that comprise that weight is irrelevant. Now getting to the 3 vs 3.5, if you compare apples to apples so to speak and use the same shot CHARGE in both samples (ie 1 3/8 oz), the 3.5 will give you more range if you have a higher powder charge with the 3.5 inch shell. FieldDressed makes a good point about the shooting abilities of shooters and their ability to judge distance. Practice will kill birds, not shell size. Ive got a good friend that I hunt with in Arkansas. Every year he brings his 20 guage out and slaughters ducks. The 3.5 is very useful for geese because you can throw so much steel, you get a lot more T's and BB's in a 3.5 in shell. For ducks its not necessary, but I can see why somebody would want one. Hope that helps. Whatever you get, PRACTICE!