I tried your route… I get mostly my stable 37.5 fixed vsync limit. But there are seemingly some regions which cause lower-fps. We assumed already long ago that it depends on some regions and that may match with the fact that in my case the fps comes allways back to “my normal” if I leave these lower-fps-regions ( or the ‘unknown’ condition which cause that ). Also, because I not realy enjoy such long flights in AP mode, where I simple have nothing to do, I worked in parallel with my pc , may be some short hicks come from that. Usually I sit in the airplane and fly that thing, and not look AP kino.
A good example is the location near JOH ( the last part in diagramm where fps jump ), may be when these ilands come into the image.
37 - 29 - 37
With this test I can not ensured conclude a timing factor.
If I have again bit time I will re-test and start from PANC.