The 600 fpm and 360 fpm impact are found in Part 25, all transport category jets have to meet those standards. Boeing used to let the airline pick the MLW (within limits.) Some airlines picked an artificially low MLW as some airports set their landing fees based on the aircraft's MLW. In a prior job we had several aircraft where this had been done. We needed a higher MLW. Sent a checked to Boeing and the MLW jumped up 4500 lbs with no physical change to the plane except a new data plate.