B772,
I reckon a standard A320 could carry a 90% load on a 6 hour flight and still land with 3 to 4 tonne (just about enough for a tempo). Better yet in the Sharklet variety. Better again with the higher gross weight option. The need to carry tempo in winter would be diminished, but probably would be compensated for by a need for longer sector fuel due stronger headwinds, so nil practical difference.
Sure, it wouldn't be quite a full load, but it'd be pretty close.
With the optional auxilliary fuel tank (bringing the fuel capacity to almost exactly that of the B738) it would be a no-brainer.
And TT are not doing SYD or BNE to DPS. JQ already to ADL and PER in the A320, so those sectors are no issue.