The only real way to determine the effectiveness of your load is to pattern it at 3, 5, 7, 10, 12, 15, 20 and 25 yards. You are looking for a uniform density across the whole target area - NO pellets flying off to Fort Mudge! ALL pellets must be on the target. You will need to experiment with a variety of loads at each distance. The goal is to find the tightest load for your shotgun over the distance.
Generally, and I do mean generally, most shotgun patterns open up pretty good at about 12 - 15 yards.
In my 870, I find that Federal H-132 tends to group the tightest. RWS Brenneke are the most accurate out to about 100 yards.
Use what is the MOST effective in YOUR gun regardless of make, model, weight of shot, size of buck etc.
Watch yer 6!