etrex 10: what is the most optimal screen fields set-up?

You mean Trip Computer?

It depends how you hike. I only turn mine on for a few moments a day. I turn it on long enough to get a gps location, and then write down some of it so I can turn off the gps and conserve battery life. Here's what I use on mine:
gps coordinates
sunrise
sunset
elevation

I guess elevation wouldn't work for you.

I bring paper maps, so usually I only turn it on long enough to write down the coordinates.

Sunrise and sunset are important because they let me know when to set my alarm to wake up, and when to start looking for camp…the latter is especially important if I'm behind a ridge and can't see where the sun is.