I do a lot of farming/forestry road riding, and you can get away with far less light in that situation. Once your eyes are adjusted, it's not unfeasible to see quite well by just the light of a full moon. I've used my Princeton Tec Quad LED camping lamp on my helmet, and turned off my generator lights before. On some pitch black backroads, I'm sure that our pack of a dozen riders all with bright LED generator lights and reflective gear looks astonishigly bright. Riders from my club have told stories of the French riders at PBP, who often use lights so dim that you can barely see them approaching in your mirror; but in the darkness, that little bit of lighting is enough for them to see with.

Off-road, you definitely want the brightest and broadest light. The Supernova E3 Triple or B&M Big Bang isn't unreasonable in that sort of situation.