I have used both & after one season I went back to 3" mags. I have shot several mossbergs & most did a nice job with the pattern but not much better than my 3" Remington did. I think for the few shot extra I got it wasn't worth the recoil.

I would say this; if you go with a gun with the bigger bore diameter then you should be ok with the 3 1/2 loads. I wouldn't want to move that much shot down a standard .665 choke!

I agree with most everyone else a good tight 3" mag. will do the job just fine, oh yea before I forget check out the velocities on some of the shells out there. You might really be surprised at which ones give the most velocity!

As an example the Remington Premier Magnum Turkey Loads in the 3 1/2 “ shell shoots at a velocity of 1150 while the 3” shell shoots at 1175. You get more shot with the 3 ½ but you loose velocity at the price of having that extra shot.

I say stick to the 3” you should get a nice pattern, plenty of power and less recoil.