Have done Heathrow to Melbourne (& return legs) a couple of times now in the economy seats and they fine. I just over 6ft & have a knackered back but the journey was fine. First time was via Singapore and the 2hr break in the middle was fine. Reasonably nice passenger lounge to amble around to stretch your legs and easy to disembark re-board the plane when needed. Second time was via Dubai (I think) and was a real pain in the arse. Took ages to get into the lounge when the plane landed as we had to go through security. Then it was quite a walk to get anywhere before having to turn around, hit security again 60 minutes before take off to be sat in a dull, holding area without refreshments, toilets or entertainment. was not a happy bunny!
First time I went was weird. was so hyped about the trip only had about 6-7 hours sleep in total over the two preceding nights, then dozed for about 1-2 hrs only on the flight. landed at 6am and stayed up until about 7pm to get back into a rhythm. All in it was about 8hrs sleep over an 80hr period. It was horrible & like being drunk without any of the benefits. I kept walking into things, fell down the stairs where we were staying with relatives & could barely string 3 words together. Next morning after 16hrs sleep I was absolutely fine!
2nd trip was better, slept quite a bit in the plane and before too!
As for Qantas flying direct to Perth, that's got to be good for the company & Australia. Would imagine that the'll expand that service and use Perth as the stopping point to get to Sydney, Melbourne, Adelaide & even New Zealand too. Keeps the airport fees in Australia, provides employment etc & also may bring more tourist to Perth for a 24hr stop over instead of Singapore/Dubai etc