Well, you said airspeed and I answered accordingly. Had you correctly said ground speed and provided a link to the flight I would have looked. At any rate I did just look at the graph, the highest groundpeed was about 626 with a true airspeed (according to the filed speed on the flight plan) of 508. A difference of 118 knots, not at all uncommon, in fact according to friends who fly the North Pacific 200 knot winds are pretty common. No, I don’t know why it diverted.