The number of lens surfaces the light has to pass through should also have an effect, I would think. If a lens passes a certain percentage of the light, more lenses should reduce the total light that actually reaches your eye. A simple fixed power, using fewer elements, would be seem to be the best choice for shots at either edge of darkness. In practice, "normal" scopes seem to work fine for shooting during legal hours in most cases.
As a practical matter, I tend to hunt the early and mid parts of the day, as tracking, field dressing, and dragging deer in the dark ain't no fun for an old fat man.
