formula to work out predicted pace with climbing = experience.
and a healthy dose of Mark Lattanzi's rules for navigating (at night)
1) Traveling at night is much slower than in the daytime.
2) Know exactly where you are when dusk comes.
3) Traveling at night is much slower than you think.
4) You need to be more careful about taking and following bearings.
5) Traveling at night is much slower than walking in molasses.
6) Use bigger point features and linear features as much as possible.
7) Traveling at night is much slower than hiking with snails.
8) When in doubt, you probably haven’t gone far enough.
9) Traveling at night is much slower than hopping with a stick in your leg.
http://www.navigationtips.com/wordpress/?p=391