Dave_C : Thanx You are quite right about the miles confusion ( I come from an area of the world where evrything is in Km so not so used to miles, and certainly not two kinds of miles).
NM: Great work. Thanx and you make very convincing arguments. However, there only seems to be a difference of an extra 783 miles that need to be 'squeezed' out of the aircraft in order to make the LHR_SYD run. Now if less luggage was allowed or your calcs per pax were diminished, this in my opinion should be possible. Or how about the 777-200LR? - this would maybe also be a more attractive aircraft for BA, since they could use their current configs ( an all NCW and WT+ perhaps in line with SQs layout?)