Also note that on CX from HKG-JNB sometimes it is operated by the dreaded 34D!!! Hence no F Class.

Also note that QF also operates a 2 Class (J and Y) on the 744 it serves JNB some of the itme!!!

so BEWARE BEWARE!!!!

The ensure you definitely get the F seats you should go via BA, but I guess you want to do Europe last??

That is why I never want to fork out the extra 3000-4000AUD for an AONEX ticket as it is getting harder and harder to get maximise the F Class flights.

Also your concern over QF/CX and 744 vs 346.

I will say this. CX's F Class will BEAT QF's F Class by a mile anyday!
I prefer the 744 then the 346 or 34C or 333 in F class. But if I have to choose between QF and CX then even is cx does not operate the 744 on that route I will still take CX over QF!

I think you can do this:

JFK-HKG (CX)
Asia sectors
HKG-SYD/MEL (CX)
SYD/MEL-xHKG (Transit within 24 hours)- LHR (on CX) you MIGHt be able to get away with JNB depending on how strict they interp. the rules.
That way you can maximise the CX F class experience!!!!

In order of preference I think you should plan on maximise F Class scetors on the following Carriers:

1) CX
2) BA
3) QF
4) IB(if they still have F Class)
5) AA (ONLY use this if it is really neccesary...)

have not tried LA so can't comment and AY does not have F Class