ACA write up, albeit a few years old: https://www.adventurecycling.org/res...ng/bc-ballast/

In short, I often prefer hardpack dirt/limestone to pavement. Can ride nearly as fast, often in better shape, and generally less people on it. As it goes downhill, though, it becomes much more difficult. Took us the better part of an hour to do about two miles on one particularly nasty road in Iceland.