I checked out the IS. My criteria are off scale compared with the usual as I count shots as being perfect only when no shake is detected at the pixel level when hand held at 20m from a high resolution target. At this distance, shake is magnified and at closer distances, shake becomes less and less observable. At 1000m, from 1/800 to 1/1600s, 70% were absolutely shake free, and 30% pretty minimal. At 1/500s, 50% perfect, 33% nearly there and 17% bad. At 1/250s, 30% perfect, 30% nearly there and 40% bad. At 1/125s, 17% perfect, 17% nearly there and 66% bad.
These figures are pretty good. In general, I try to keep shutter speeds faster than 1/500s for optimal sharpness. From experience, a setting of 1/1250s, iso 1000 at 1000mm f/14 would be fine for me on a bright day.
I believe my AF/IS issues from that day watching the jets was more user error than anything else. I found that I had inadvertently had the IS switch in mode 1 when I started to take panning shots (so +1 on user error). The other was that I was missing focus occasionally probably because of IS, but also because I was struggling to keep still (handheld).
Of the shots I did like, I was impressed. For example, zoom in on the 1 plane shot and look at the face of the pilot.