i was on this flight (mid-week) recently where J section was completely full - and Y were about 40-50% full (my rough estimate). There was no availability for my RTW ticket, but one opened up at the last minute so I was able to change to this one. (my original booking was on MH: PER-KUL-LHR)
Slept like a baby for 14 straight hours!

pitch black outside for most of 17 hours.
I miss old kate spade bags ;_;