I've been going through the process of buying my first Semi and this is one of my hot topics. My buddies and myself all hunt ducks with 3" #2,3, or 4's. We also carry rather cheap 3.5" BB loads for Geese when they fly by. I've spent countless hours thinking about how big of a deal this is to me, and I've been able to completely convince myself either way.

I've spoken to lots of people that have been doing this for years and they all say the same thing, it can be done with 3's without a problem. If the gun that feels the best in my hands only takes up to 3" shells then get it, you will shoot a comfortable gun more accurately and with more confidence than one that shoots 3.5's just because it shoots 3.5's. Now that being said if the gun that fits you shoots 3.5's then why not, but since you already have a great shotgun keep it and use it. I think you wouldn't have any problems with the 3" BC BB's dropping geese like rain.