The Xikar Purofine High Performance butane is the best out there, especially for high altitude. If you have any lighters that have a low flame or no flame problem I highly recommend you try this product. No I don't work for Xikar.
I ended up picking up am IM Corona Old Boy at the Stag Tobacco shop in Colorado Springs on my way up the mountain. They fill all of their lighters with High altitude butane. The Old Boy worked like a champ.