Doing this about once a month. The seats and service are about the same as shorter routes. Lunch and dinner are indistinguishable. Usually the old 767's (ex Ansett?) with the shrunken overhead bins so board early.
Whereas on SYD-PER, they sometimes put international-configured aircraft on the route and there seems to be more food & drinks loaded, better choice of wine etc. No amenity kits though.
And, if you take the last flight from BNE at 7.50pm this seems to get the lowest priority, the GAs get every other flight on the road before boarding QF767. So it's usually midnight Perth time before you're out of the airport.
Also the J lounge is usually packed ahaed of this flight, to the extent it's usually more comfortable next door in the regular QP.
Still, it's a comfortable 5-hour service in J which would be unbearable in Y.