I agree with CL300... "Certification during emergency descent is a limiting factor, even with ADM".
That's why the Challenger 601/604/605 and 650 are restricted to FL410.
We fly our Globals between FL410 and FL470 all the time (FL430 and FL450 being the most often used)... On flights from Europe to Montreal we will start at FL430 climb to FL450 at 30W (if ATC allows it) and climb to FL470 prior to coast in with Gander on our way to CYUL... A few times at FL490 but that was on a very long flight like Beijing to Montreal.