Diluter-demand oxygen systems can be used up to 40,000 feet. In a pressure-demand system, oxygen in the mask is above ambient pressure, permitting breathing above 40,000 feet. Because the pressure inside the mask is greater than the pressure around the user’s torso, inhalation is easy, but exhalation requires more effort. Aviators are trained in pressure-demand breathing in altitude chambers.

1. Which system do the 777 pilots have - diluter or pressure demand ?
2. Discounting former military pilots, what % of airline pilots get altitude chamber training and high altitude physiology training ?
3. How big an IAS envelope is there between stall and Mach tuck in a 777 at 45,000 ft ?

My questions don't imply anything - just looking for answers.