Larry, the main problem I see with using smaller shot, such a 9's is that most of us aren't able to consistently hit our birds with the center of the pattern. I often only hit them with the fringe of the pattern. Using the 7's one pellet is often all that is needed to penetrate to the vitals but a single 9 seldom has enough energy to put a bird down hard but they fly off to die later. Now, all I shoot are wild birds and the action is quick and often unexpected and on very uneven ground with mesquite trees everywhere. So, quick intuitive reactions are critical and no time to plan where to center the bird.

When an old man dies a library burns to the ground. (Old African proverb)