On CX a 34C is also OK (3 class), as is a 77A (new long haul 777-300ER)

BE careful with HKG-SYD - CX is withdrawing F from that route over the next year or so. I'd go with QF to be safe.

However, note that changes of carrier are free of charge on OWEs so no worries (assuming availability) if you want to switch that nearer the time.

If you don't need to go to SYD before ADL as well as after it then you can save a segment by flying HKG-ADL-SYD-CHC if you're propeared to take the risk that CX is still flying F to ADL when you want to go. (Remember that if you book a confirmed flight in F then you should get either a free reroute or compensation if CX subsequently withdraws it on the route.)