Okay, how about this...?
LHR-BKK/SIN-SYD on BA: 120000 miles for J
LHR-HKG-SYD on CX: 120000 miles for J
LHR-BKK-SYD on QF: 140000 miles for J
(All awards on AAdvantage)
Flying BA or CX seems to be definately the best option. It's only 15000 miles more than LAX-SYD on QF and it's a whole load less hassle (and saves you having to be on coach for many hours.
And many people will agree IMO that CX is on par, if not better, than QF!

Not to mention their "The Wing" lounge in HKG, which is (supposed to be, haven't been myself) simply amazing!
BTW, Compton Sid: It's just not worth even thinking about getting an upgrade on CX. They actually care about their premium products!