La Sportiva Spantiks, used to summit Denali, spent 2 weeks in them, thats it! retail for 750$ asking 575$. They‘re amazing boots for any 6000 or above meter peak, or even for an especially cold day on a winter 14er. Can even be combined with Silveretta bindings for ski mountaineering. They are especially warm and great for anyone with previous frostbite or who worries about getting it in the future.