The 9mm does seem big to me; but the 8mm seems so "normal". I think 8.5 would be my Goldilocks size, but I can't get an inexpensive stone that size.
I took my husband to a jewelry store to see an 8mm set (no one carries any larger that are set around here) and he wasn't impressed, said to go 9mm. Well, we'll just have to see!
I'm not really "frank" I just play him on the forums.