My advice if your decoy step up and topography allow it use #5 or #6 steel with i.c. or a more open choke. This last year the water on the river was way down shrinking the size of the back water we hunt all shots where under 30yds. Think of it this way we use extremely small shot relative to body size for turkey. The reason being we aim for the head. The small shot fills in the pattern and the open choke gives you a greater chance of multiple hits to the head/neck of the duck. #6 will work just fine for mallards.