I think whatever gives you the most complete pattern in a 15" circle at 40 is the way to go. For me, shooting number 6 LB.s it was the Remington Super Full turkey choke out of my 870 with 26" barrel. I hit 148 in the 10 circle and 203 within the 15" circle. That allows for a bit of wiggle room if the sucker moves his head a few inches at the moment the trigger is pulled.