That is true. I guess it depends on the rotation speed at the time of the shot. I had read 1/320 but like you I have had to go to 1/160 but it gets a little shaky for me even with IS.
On take off I imagine they are spinning the prop faster than the flybys during the shows, I wanted to go slower as I got used to panning but old age is catching up with me. I started at 1/250th but next time if I go I think I will start at 1/160th, that way if I have to quit early again I still should get in a few decent shots.