i think it has more to do with size/mass than BF%. personally i barely work my legs (or at least just started up again recently) and they are about 23 inches or so, and pretty hard, and i'll be damned if i stuck that long ass bitch in there. 1" for me, or i'll hold back on the 1 1/2" in a pinch.
yes I do.. it is fine, unless like noted earlier, you are a fucking fat ass... than you may need more. I would say if you are under 20% BF 5/8" is fine.