PER-MEL early 80s. As I recall about 230kts tailwind component in the jetstream for most of the flight. And I still have a pix somewhere of a QF 74 overtaking us a couple of thousand feet above .. at the end of the sector (which was a freight leg) we did a run over the intersection to finish the timing. Can't (won't) recall the actual height .. but we were told after landing that it looked good from the ground.