sorry, I am trying to change my profile pic, and not having much luck. (It sez it cannot take the pic,... its small enuff.) geez !
Anyway, I went to a smaller diameter shaft yrs ago when I was playing as a teen. The advantage is that (IMO) you get a much cleaner sight-line (I think they call that CTE now) to the OB when you line up with the CB. I had problems doing so with a 13mm shaft. That got clear when I could plant a bead easily with an 11mm.
There are 2 small disadvantages that you may want to consider.
First is stroke, the narrower sightline to the OB will magnify any imperfections in your stroke. I get caught when I'm not cognisant,.... usually when i'm tired in a tourney.
second is there is a lil less real estate on your tip, something to consider for sharp angles,(hard cuts), and to a lesser extent English.