I took the liberty calculating classic B747 takeoff weights for Manchester, also ran a couple of Jeppesen CFPs to Pakistan. @30C the -300 is performance limited below the structural weight. If these flights are full they will be right on the limits.
Notso Fantastic, i guess that you were lucky that the VSI was on the positive side.... we have had flights out of that part of the desert recording a descent after takeoff, with 4 engines running!
Mutt.