I wouldn't care about the 3 1/2" capability, 3" is all you'll ever need. I'd go with the shorter barrel if you had the choice. I'm using an 870 express now, and the 28" barrel is a bit long for turkey hunting, especially when coupled with an extended choke tube. If you can get the supermag with the shorter barrel, it would be worth the extra few bucks instead of shelling out a whole lot more fora differentbarrel. Just because its chambered to be able to shoot 3 1/2" shells doesn't mean you have to shoot them.