Kurt Ullman wrote:

The plane would be stalling at 45k feet. I've heard some pilots
say that anything over 40k feet is a crapshoot in terms of being
able to keep a plane like that flying.

The rated ceiling for the 777 is 43,100.

With what?

No passengers and maybe half a tank of gas?

How about a full plane, with a huge load of avgas for a long flight?