I promised my explanation, so here it is. The reason I think my memory did so well up high on Everest is because of something that actually has nothing to do with actual memory. Because we slowly entered (hiked) into Everest Base Camp and beyond, everyday normal things slowly began to vanish. Things like certain colors (green, pink, purple, etc), certain smells (good food, earth, flower, animals, etc), and certain sounds (rivers flowing, thunder, rain, etc.), they all eventually became non-existant with my progressing elevation.
So with that in mind, I believe that my senses became dulled. At 17,000 ft (Base Camp) the air was so thin and lifeless, nothing around me was exciting (aside from the amazing snow and mountains, but even that lost its luster after a couple weeks). When I sat down to do my training, it served as an escape to a more lively, sensory stimulating world. Everything stored in my memory became greatly enhanced since it contrasted so much from my surroundings. Because of that, I believe that when I would memorize the images that presented themselves in my mind were that much more memorable and vivid, thus "sticking" better and forming quicker.
In brief, I don't believe it was my memory per say that was improving, it was more so my visualization skills (which I guess you could argue IS a large part of memory).