Bamboo? I am SO jealous. Never done bamboo. So where'd ya get it? I've got corn silk but haven't spun it yet. Here's my very uneducated guess. Draft thin w/ lots of twist. On those long fibers, pre-drafting was important for me. Otherwise I couldn't draft fast enough. Ended up w/ a big thick single. Split it down the middle if that makes drafting easier.
Pencil roving: It's all a matter of taste dear. And yes I draft my pencil roving. I have yet to get fiber that didn't need to be drafted.
Pencil roving is prepared fiber that has been drawn through a diz to produce a thin, compact fiber.
I may be wrong, but I don't think it's any easier to spin than any other form of prepared fiber.