Yeoman,
Your question about multiple performance points is not unusual to see. In reloading for CF's I have noticed similar grouping at different powder levels with a spread between. It can to some degree be related to barrel harmonics. Every barrel vibrates when shot in a circular fashion. The point at which the bullet exits the barrel during that vibration determines to a great extent where the group will end up and how tight that group is. If you find two loads that exit at the same point in the vibration cycle you will have a good chance that they both perform well compared to other loads in that gun.