Why do you ask? The big issue with some of the earlier 3 1/2 in guns is reliable cycling of lighter 2 3/4 inch loads like for clay shooting. Sometimes a certain brand of ammo will cycle and another would not. Most of the newer models of the last few years do pretty well with that now. You may get unlucky and have a 3 1/2 that is picky or has problems with the lighter loads, where 3" guns that do that are rare now.
I bought a Remington 870 Wingmaster Super Magnum 3.5 inch about 6-8 years ago. Seems to shoot all loads OK. I havent seen these guns advertised in 3.5 from Remington in catalogs or website for the last few years. Has there been troubles that they discontinued them?
Like someone sort of stated already...Better to have it and not need it than to need it and not have it. I love my 3 1/2" chambered guns (SBE II and 3 Mossberg 835's) Every one of them shoots and cycles 3 1/2" to 2 3/4" loads equallly well. My Thumbhole 835 turkey slayer puts up patterns with 3.5" hevi 6's and 7's that most guys dream about being able to get in their guns.
when I went to leave for college my step-dad decided I needed my own shotgun instead of taking his old 20 gauge with me. He bought me a new Mossberg 835 Ultra-mag and sent me off into the world. It does it all, bunnies, pheasants, turkey etc. Having it first I have bought other guns that only take 2 3/4 or 3 inch only because if I need something with a little more umph I just take the 835. Like a mechanic, doctor, or dentist different tools for different jobs. At least thats my reasoning, my wife just says I like buying guns.