keep it light, get something wide (if you are a wide shooter), you could go cheap and get something like the compact, light and sturdy zenitar instead of the (excellent) 12-24, but keep in mind the zenitar is the sort of beast you need to get used to. maybe consider some solar powered solution to recharge the li-ion's, if you will be there long enough, and pack some spares in any case. polarizers are light and small, so you can take them, but i doubt you will have any use for them at such altitude.
i am stubborn and always bring my tripod on my hikes (never hiked with a light pack, wonder how that must feel..), but i don't usually go in the vicinity of 8k m

), never considered a monopod, interesting point.
stepping back a little, i might start by thinking what i want to shoot, before deciding what to bring (only landscape at base camp? how about vilages on the way and people there? etc), you might find that you do want that 50/1.4, or a longer lens for non-intrussive portraits. i tend to use longer lenses for landscape too, so for me leaving the tele at home would be pretty much out of the question anyway.
do not underestimate what 1kg more/less means when oxygen is hard to come by...
good luck, and be sure to show us what you get
nanok, walking away green with envy
edit: you might want to consider a light, all mechanical, k-mount film body, depending on how compatible your chosen lenses will be (meaning, if they have an aperture ring), and a few rolls of film. you never know, it might save the day