DJ Dan, I shoot Hevi Shot in my SBE II both over Decoys and in the field. Modified may be starting to get a bit out there for 50 yard honkers. I would go with a Briley extended IM for that distance.
As for the Hevi Shot. 6's are good for ducks, 4's for Snow Geese, and 2's should be used for the big boys at that distance.
Good Hunting.