Some time after BA had fitted -7's to their 747's we leased a 747-100 from Aer Lingus, G-BDPZ (known by the crews as "Paddy Zulu") which had -3A engines.
On one occasion we had a rather close view of the far end of the runway and had great difficulty making our cleared levels. In those days we used to entertain passengers on the flight deck and we had most of the 400 passengers visit us (not all together)(PZ had 404 seats). We soon realised what the problem was.
An American farm buildings company had run a competition amongst farm workers and the prize was a trip to London. We had 200 prizewinners and their partners on board. To put it politely, the average weights did not apply to this group. Added to that they had all had a rather busy time in the shops and the duty free. Our (official) take-off weight was only a few kg under max. I dread to think what the actual weight was. The trip fuel burn was higher but fortunately in those days the reserves were higher so we made it to Chicago.