This is good, but I think the "most likely estimate" is going to be misleading a lot of the time. I don't have numbers to back it up, but I have a strong sense

This is good, but I think the "most likely estimate" is going to be misleading a lot of the time. I don't have numbers to back it up, but I have a strong sense that the actual time to completion tends to be either at the quick end or the slow end of the estimation range, and only rarely somewhere in the middle. A bactrian, not a dromedary. If we hit the problems we were anticipating we might then the whole thing can take ages, but if we don't hit them it's pretty quick. Best and worst case are going to fairly predictable in advance (the latter improving a lot with experience) so I'd stick with just those personally.