Agree - wait times in the TBIT premium lines can be very long. They let all the wheel chair and families cut in front of the premium lines. The regular lines are long but move just as quick.
You may be able to do boarding pass in advance for QF as well.
My currently thinking - get your QF boarding pass as the QF counter in TBIT then walk back to T4 and go through T4 security.
The QF F lounge (if eligible) is at the same level as the connector. Just continue pass the down escalator after you enter TBIT via the connector, and the QF F lounge is the first thing you come to.