By £50K avios do you mean 50k or is it a different typo. I'm afraid 50k won't get you very far, so the Qatar option would be most sensible if that's the case. And I assume by further spending you're talking about tens of £ks not £100k which would get you somewhere on other airlines?
If you had the avios and the voucher you would need to be booking a Jan19 flight for SYD this month, not in March (adding the return later). Other than booking the seats on release (T-355) you're very unlikely to find anything outbound.
Last edited by pauldb; Jan 5, 2018 at 6:47 am