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Where would you be starting such a trip from?
MEL-BNE-CNS return in Flex Y for example would get 120 SC and could be done in the one day. Flying indirect is typically better value than flying direct.
Have you got a loyalty bonus for passing 500 SC on QF flights yet and if not are you close to getting that? There is the option to take 50 SC as the loyalty bonus. If you haven't yet got that or chosen your bonus (if you qualified for it recently and it hasn't yet expired) that would reduce the SC you need to get from flying.
This is pretty late to be planning this. There was a DSC promotion earlier this year. There's currently a 50% promo for QBR members (but that requires an ABN and that the travel be for business (see 50% more status credits with Qantas Business Rewards to 19/6)