Boeing build them to withstand a no-flare landing ie upto about 800fpm on a heavy weight landing.
Good landings on the 747 are when you eliminate ALL drift and the final descent rate is such that the spoilers deploy at the end of the touchdown. If you hold off the main gear, when the trucks are no longer tilted (giving an a/c on ground signal to the spoilers) you will end up dropping another 2-3ft spoiling an otherwise great touchdown.
No figures, I'm afraid but you know when it's a good'un.