My thoughts on QF 9 having just done it.
Narrow seats are horrible. Seat padding for the bottom is too hard. Sore bum. Storage places and IFE are pretty good. Timing of the flight is pretty good.
PER airport going through security twice is annoying. No priority queue for the second lot and no fast track immigration. Transit lounge is a bit naff. The "outdoor" area is just an open roof area, but otherwise fully enclosed. So just makes the entire lounge noisy with aircraft noise. If you want to actually have a meal before your flight, the fancy hot dog doesn't cut it. Better off stopping in at the domestic J lounge on the way through (which you're entitled to do if you have lounge access).
All in all, if you're needing to get the LHR from PER in Y. It might be worth considering. I needed to connect to TLV and went this option as I was hoping for a points upgrade and CX via HKG had a long layover. Next time I'll try CX and just hang in the F lounges there instead. The BA F lounge in T5 is nothing special. I've been in nicer J lounges.