I flew PE and returned in J (BA), ask them to have a bit of mercy and let you fly CW, but PE in BA is fine, leg room is decent.... bit annoying if you have someone in front of you, so try to get a seat by the exit door.
I'd take the A380 into sing and take the 777 to sydney if possible, same on the way back. Otherwise Cathay is probably the better choice, plus you get treated better because of gold and excellent lounges in HKG.