I have just flown LHR - SYD - LHR on BA tickets but QF outbound in PE and BA inbound in WT+. I am 6'4" and found the QF PE seat MUCH better than the BA WT+ seat. I agree with LTN Phobia about WT+ on the highJ 747... both 28B & J and 29 A & K are great for tall people.

My only other comment is that IMO CW is miles ahead of QF J. That truly hideous offering that QF call their sky bed is only marginally better than their PE seat. So if you get upgraded to J on QF IMO its not a scratch on being upgraded to CW

Finally, if you fly QF then book QF, if you fly QF on a BA ticket OLCI is a mess and you can't select seats.