DHD, that 20 knots difference in wind when QF is (say) 15,000 feet lower translates into about a sixty knot+ difference in ground speed due to higher TAS @ FL280 (depending on the day of course!). As you would have read in the newspapers, schedule is a pretty big issue at QF these days and so saving 5 minutes on a SYD-MEL leg can influence things over the period of the day.