I would not be crediting to Qantas versus just credit to existing account. You can redeem for domestic flights from that
If you have no status, you might like to consider crediting to AA and taking the Platinum challenge. This would get you Platinum status ( valid for rest of 2017 and all of 2018) just from the LHR-SYD journey and points which will be more valuable with no surcharges to pay on redemptions ( other than for BA redemptions )