I've done a fair amount of patterning...
Mild weather during the early season I will use a IC with 5's when the birds are sitting a little tighter. As the season progresses and the birds become wilder and gain their winter coats I often will switch to modified and #4's. If I stay honest on my ranges and keep my shots to 40 yards and in I've experienced very few cripples with those combinations. I've done a fair amount of patterning and know that if I do my part very few birds are going to fly through those patterns.
I must add that the differences I've experienced between #6 shot and in some cases #5 and that of plated #4 shot is astounding with regards crippling and lost birds. Now that I am using #4's I experience far fewer cripples and are usually dead where they fall. The pellets seem to penetrate all the way through leaving few if any cut feathers or shot in the meat as well.
I've no idea what the thinking is behind extended tubes.