I dunno about starting from SYD and doing that route via MEL, maybe SYD-PER-LHR would make more sense.I have a friend who flies the PER -LHR on a regular basis in J. He loves the direct flight and thinks Sunrise is the way to go whilst I think it sounds like a special kind of hell devised by a mathematical bean counter. Then again I miss the days of the stop over in HNL which was often an excuse for a day at the beach.
Of course the great irony is that his trip usually always starts in SYD and is often SYD -MEL - PER - LHR (and sometimes SYD -PER-LHR). He swears its a direct flight to LHR. Go figure. I'd prefer a shower in SIN.
I think these long haul flights (from a passenger perspective) are more beneficial to those who struggle to get to sleep on planes than those who can fall asleep anywhere any time. In business class (SIN-EWR-SIN), I've found them extremely good from a rest perspective, you don't have to try to force yourself to sleep at a specific time dictated by when you will transit another airport. I sometimes struggle falling asleep on planes, even with lie flat seats, and hate just falling asleep and being woken an hour or two later for that transit point, and then taking ages to fall asleep again after taking off again. Even in Y+ (SIN-LAX-SIN), found it better than transitting NRT or ICN or the like.
For SYD-LHR route, I can see the non stop being superior to flights where you have a relatively short hop before a 6am arrival (such as SYD-DXB-LHR or LHR-SIN-SYD, but less advantageous compared to the sectors where you have a long hop before the 6am arrival (SYD-SIN-LHR, LHR-DXB-SYD). YMMV.