ah the darwin stubbie
Firstly QF make you think... what flight rules?... as you will be flying 310-335 degrees mag depending on the leg that's point 1. Then it's a subtle dig to see what you know about bouncy animals aicraft that actually go YSSY-YPDN. There's the world of difference in what a BAe 146 Quantas Link a/c can do and a 737. Next are you flying RVSM or following the old IFR? Then give a little elaboration; if RVSM can your aircraft get to FL400 a) at all b) profitably in the four or so hours you have to QF it. The answer might well be FL360 bearing in mind what everyone has said about FMS, wind, cost index etc. (If not RVSM then substitute FL350, FL390). Basically you have say 4hrs 15mins to get 120 happy pax YSSY-YPDN getting the most air miles for the least fuel. Fly fast enough to meet schedule but not so fast that you consume too much fuel... that's called V/c ratio. Next you need to fly with a good lift:drag ratio... that's L/D. Multiply the two together... VL/cD gives a figure of merit. When it peaks you are doing it right providing weather, wind, law and ATC permit.
By the way when you get that job lob a stubbie out passing Mudgee (MDG) on your way to Darwin and be prepared to explain the difference between a Mudgee stubbie and a Darwin stubbie. Best of Luck!!