Oh god I couldn't think of anything worse... just glad I am retired.
Probably not to bad if you are in F or J, horrendous down the back. Awful for the crew.
I for one much prefer to stop off for a day on the way going down under.
In my flying days I had a couple of deaths on Aussie routes, lots of older folk visiting relatives, sitting cramped for hour after hour. Can't imagine what a flight that long would be like