Depending on how tall you are, AC's slaveship configuration in economy could absolutely be physically painful on an ultra long haul like YYZ HKG. I'm not trying to be dramatic here. I fly long haul in economy all the time, and AC's 777 and 787 configuration is noticeably less comfortable than pretty much any other major international carrier. It's one thing on a transcon but quite another on a 15 hour flight.