Remember every slug gun is like women, All are the same but each is a little different, Some are keepers and other's you need to stay clear of. All are unpredictable.
I have all ways said if you have a combo that works good for you stay with it. Keeping that in Mind remember all so that I dont get along with Remington and Savage because of there Department for gun repair and specks. All though I have many friends who shoot them both and would not trade for the world.
If your buying slugs there is a difference in ammo. Foster slugs, Rem is the smallest diam, Followed by Fed, Win, You need to try to find which your gun likes best. I have had the best luck with factory ammo in the Brenneke and Active foster slugs as wad is attached to the slug and goes down range with it. Like feathers on a arrow. Sabots even seam better. Personaly again I dont care for the Rem but have had folks do very well with them. Fact is Factorys load the 3 inch a little more powereful as there mostly new guns. So is a little safer for them to do.
I reload and Manufacter slugs for me and family, etc. If you have a new shooots gun and it is quality made. You can up the psi but I dont go to max as thats too much danger in destroying a nice fire arm. The reloader all so can get the same ballistic's with a 2 and 1/2 as the 3 and 1/2 with the modern powders. In most cases the difference is in the length of the wad. Thats it. It has nothing to do with the case capacity or length. You just very the wad length. I load and shoot the 2 and 1/2 in reloads as It gives me two more shots in the 3 inch tubes. and all so I can easyly I.D. the slugs as there the 2 and 1/2 length. I use star crimp on cast Sabot slugs,
All so remember that any thing I have said goes out the window if your going to shoot shot with the same barrel. Thats a whole new ball game.