I'm no SC expert to/from AUS, but if you want to come through the US, pick up some YUP fare (Booked as F or P) from AA.
eg LAX-DFW-JFK then JFK-DFW-LAX for $1300 US and this will get you 480 sc.
You could also drop in another stopover for the same money and pick up another 180sc.
I went SYD-MEL-SIN-LHR instead of SYD-LHR a few years back, earnt me 75 SC's instead of 60 - was back before fuel surcharges applied by the sector were in operation though, so it may make it less worthwhile....
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It depends on the class of travel. If business class, then seriously consider as OneWorld Explorer fare which is often cheaper than the point to point business class fare.
Another great option is to use the BA World traveller Plus fares, and with their current special deal of paying for WT+ and flying one-way in Club World (business class), its even better.
With the new SC earning tables, the different routings don't make a lot of difference now. For example, SYD/MEL-SIN/HKG/BKK all earn the same SC's (30 in discount economy, 120 in business class). And BKK/SIN/HKG-LHR all earn 40 SCs in discount economy and 160 SCs in business class.
If you do as thadocta recommends and break the journey into multiple segments (ie coupons or flight number on your ticket) then you earn a little more than routing on the through flight SYD-LHR.
Another option is to go SYD-SIN-FRA-LHR, but again make sure its two separate sectors SYD-SIN and SIN-FRA and not just ticketed as SYD-FRA.
Better still, try to go SYD-NRT-LHR since the first sector is over the 4800 mile threshold and the second over the 5800 mile threshold, thus earning 35+40=75 SCs each way for two sectors. However you may not get the same fare by routing through NRT, and the connections may not be as good as SIN/BKK/HKG.
I still think BA's WT+ is the best option, earning full economy SCs, so going SYD-SIN-LHR would be 60+80=140 SCs each way. Just make sure you take different flight numbers on each segment, or stopover on SIN at least overnight. And these fares often include a European connection, so you could add something like LHR-ATH-LHR at 1500 miles each way, you earn an additional 40 SCs for the effort. Though they may not permit the longer European flights on some fares. But look for something more than 600 miles to get at least 30 SCs.
Thanks for the hints. They have been a great help at looking at the challlenge in a new way. I agree that WT+ looks like a great option since I am paying for the trips and finding the crush in economy tough when you have to get out and work the same day as arrival.