I recently flew with QF in J before flying on BA16 to LHR. There's no disputing that it was nice. But do consider that BNE-SYD is just over an hour, as is SYD-MEL. BNE-MEL is just over 2 hours. If you want to reduce cost a bit, flying in Y may be an option, especially if you have frequent flyer status and can get lounge access.