I've heard that spicy food can increase circulation. I don't know if there is much truth to it or not.
I also read a book, "The Secrets of Warmth" I think it was called. I don't remember the author, but he wrote about how you can help increase circulation with cold and hot water baths. I don't remember the specifics, you should check that book out before running with that one. The book was mostly stuff that most anyone who spends a good deal of time in the cold knows, but it might be worth a quick skim. I found it at our public library.
The thing that has helped me the most is keeping a really close eye on my heat level and decreasing the amount of insulation to keep myself from sweating too much and getting my insulation damp. Keeping your core warm goes a long way to keeping the hands and feet warm. Not that I've ever been anywhere near as high as 6500m, except in an airplane.
If women ruled the world there would be no wars, just be a bunch of jealous countries not talking to each other.