Funny, I wasn't thinking of a Bus.
I was thinking of say.... G4. Civilian Svc Ceiling is FL450. Military ceiling is FL510. Depending on the version, service ceilings can be quite different in 'normal' airplanes.
Yes, the Bus gives you a little more 'help' if you want to call it that with Alpha floor and Alpha Prot. But even that will bite if there is a pax onboard named Murphy.