Yes, I have given up on the code share.
By changing my arrival day I can find an earlier second domestic departure, which gives me, at worst, five hours at BNE which is fine.
I will book the second one and, if early arriving, see if I can get on the 8.10. It certainly helps that Qantas have a domestic check-in at the international terminal.
The EK434 is consistently and significantly early - in at 5.56am this morning. In April I was from the plane to outside the airport in under twenty minutes.
Thanks for the advice.