In my experience, following distance setting makes a big difference in Autopilot's aggressiveness and therefore efficiency. If you want Autopilot to be more efficient, you have to give it longer following distances (and accept more idiots cutting in.)
For a while, it didn't matter what following distance I was using (3, 5, 7), it was trying to keep that distance as quickly as possible without any type of deadband that led me to think it wasn't great on efficiency. Its now using some type of filtering/deadband to that makes it much smoother.