To get the required range out of the GV on 6000nm legs you have to spend a good portion of your time in the upper 40's, FL 470-FL490.
The aircraft has an automatic emergency descent mode under certain conditions. If your above 40,000 ft with the autopilot and autothrottles engaged and you get a cabin pressure low alert, the aircraft will turn 90 degrees left of present course, it will descend to 15,000 ft at MMO/VMO and level off and it will then maintain the current heading and a speed of 250 kts. If you have a rapid D you have to get your mask on and you must get the speedbrake out in the GV. The concern I have is that at FL 490 you may not have time to get your mask on, this is why the regs say above 410 one person must wear the mask at all times. The airplane will descend around 7000-9000 ft/min with the speedbrakes out but MUCH slower if you don't. All the occupants are going to be seriously injured if they survive at all. This is not a comforting feeling for me while cruising at high altitudes.