Thanks for all the replies. My experiences with 00 buck described in the OP are a bit small (n=1) so I won't make too many judgements from it. Before the shot, if someone had told me that runt deer would travel more than 10 yards with that hit, I'd have called them crazy. It's just a load of energy and a LOT of holes in a deer for it to make it that far. That said, deer sometimes seem like they are quite easy to drop and other times make it a long way with good hits.
Still sticking with the buckshot for HD.