FM,
Himalaya 100 is a stage race, with one day being a full marathon. It is held at heights up to 11,000 ft, if you do a google search you should be able to find it, if not, and you are interested, e-mail me, and I am sure I can find the site address.
Impressive peaks. I've done Kilimanjaro, and doing, I hope, Mont Blanc, in four weeks. I do fancy Aconcagua at some stage, and then maybe Cho Oyu