Hey Skipper, not all 707's had a service ceiling of FL410, some did, some didn't.. I bet modifications were made to climb over FL400 or came with an option with modified engines and wings.. I searched through Boeing's site, some were certified out of the factory with a service ceiling of FL360, some variants had a higher ceiling.. I guess it's what Captain sim modeled, if you're rocking, means too high for weight.. No reason to fly more than FL350/360 on a westerly heading  in Northern Hemisphere anyway..  ;)