Please re-read my explanation carefully:
- If the airplane communicates the number of passengers to GSX, the payload won't matter, and the number will always be correct, assuming the airplane code is communicating the correct number. This is not the case with PMDG, which doesn't support this.
- If the airplane doesn't communicate the number of passengers to GSX, the payload WILL matter, so GSX will have to know the correct (final) payload before creating its vehicles.
- If you disable the "Estimate Passenger Number" option, the payload won't matter anymore, and GSX will ask you for the number of passengers each time it needs it to calculate how many carts to display, how many passengers to show, etc.