My last comment on this (probably!) - You do realise that you aren't comparing like with like? Astronauts were using oxygen and space-suits to enable them to survive on the moon. Mountaineers, as you say, have climbed to 8000m without that sort of support. I'm failing to see how (and why!)...
Eh? That statement isn't true. I'd assume (IF this 'death zone' exists) it is meant that without oxygen it may be almost impossible. Try it in a space suit - you'll be fine.