Just use a factory full and get good shells. if you don't kill em out to 40 yds it ain't the guns fault. super dooper tight patterns are great for long shots but most turkeys get shot under 30 yds....I bet for every bird killed at 50 because of a super tight pattern there is one missed at 15 for the same reason.
I have used 3.5" 12 gauges for turkey hunting for awhile and they will reach out. I haven't killed a longe range bird with my current setup that I have hunted the last 2 yrs with ( Beretta Extrema2, fact full, 3.5" Winchester HD number 5's) but my last setup that I toated for 12 yrs was a 835 and I shot 3.5" federal lead 5's...Killed several birds wayyy out there with it. One I shoulda never shot at was 64 paces....I shot it running after my buddy made his strutting mate flop at 30 yds...Killed a couple others at 50ish yds after other people missed em closer.