A point of clarification is required here I believe- High J on the 747 is 70 Club World across the Upper Deck, and two separate lower deck areas of J class seats. Mid J as I think the other term is now referred to is 52 seats, Upper Deck and the more central of the 2 lower deck areas. Premium Economy in these latter aircraft is in the old Zone B i.e. directly behind First Class. So in reality in a High J configuration, Premium Economy can often disembark before lower deck seated J class passengers.