Mostly use a 20 ga and am fine with 5s or 6s lead. Generally an ounce in either 20 or 16 and 1 1/8 if I break out the 12. I tend to prefer lower velocity rounds for better patterns.
2 3/4 5 or 6 what ever is cheap alot of times it will happen to be what ever is in the center counsel while out driving around and seeing a chicken in the ditch
Winchester Super X 1-1/8 oz #6 out of a 16 gauge is pretty much all I shoot. If I'm on an area that requires non tox I'll use Boss #5s. If I miss them with either of those, a bigger pay load wouldn't change anything.