You could probably do 400k okay without too much effect of sleep deprivation. Just keep the coffee coming.

I found that getting very tired led me to feel extremely cold - that was hard to get over even after it warmed up. So I'm thinking maybe bringing even another layer for the "wee hours" when it is bone chillingly cold. And keeping the layer in a plastic bag to ensure it is dry is essential.

You get stupid, too. I had a plastic bag to keep my extra shorts dry. I just took them out for some reason and left them out, in the rain. Duh. You just have to try to ensure your stupidity is limited to inconveniences like that and doesn't become life threatening.

Boy, I'm not doing a very good job selling this, am I?