A couple of months back, booked BA F (BNE-LHR) via SYD with BNE-SYD in QF J for less than booking QF J. QF F was way over the top. BA F is on 15/16, so 777 the whole way.
Did this after much research and watching, then got a real surprise when booking (via AMEX online, to use a travel credit), when for some strange reason it offered QF2 (in F) for the final leg SIN-SYD at no different cost to the BA flight. Jumped on that - both to do a back-to-back comparison (come off BA15 LHR to SIN straight on to QF2), and for the extra SC and points. Crediting to QF, BA F LHR-SYD (or v/v) gives 210, but BA F LHR-SIN gives 180, plus another 180 for QF F SIN-SYD, not to mention the points earn gain.
Not flying this until July, so will also experience the updated BA F soft product, which may swing the balance some more.