My 3"X3" model is fine with shotshells, especially around 5 yards, nice and tight pattern. My favorite HD load is 3" lead BB, 35 or so pellets that will cover a 12" circle at 5 yards and have decent penetration.
Slugs suck, don't waste time or money on them.
.45 Colt is superb, out to 25 yards I can keep all 5 inside 5".
Yep, plenty loud, but recoil is no problem as this pistol is plenty heavy.
I don't think I would enjoy the 6" barrel as much, It's a long gun already.
Gobs of fun to shoot and does all I hoped and then some.