You sure? A year or two ago, a 772-LR did HKG-LHR nonstop flying eastbound, 22 hours. Granted, it was with the prevailing winds. My understanding is that LHR-SYD would be no sweat, but the return might require a stop. Here's what Boeing has to say. 772-LR London Range Map. This assumes three "standard" Boeing installed auxiliary fuel tanks. Seems to me that there would be enough demand to support this flight on a 772 (but I have no hard data and am just guessing). The aircraft is smaller than the 744s and 773s. Eliminating the stop in HKG, SIN or BKK would save hours. Nonstop, cruising at Boeing's published cruise speed of Mach .84, flying time would be 19:05. Flying through either BKK or SIN, including time on the ground, total elapsed time is approximately 22:20.