I play with 13MM and change out shafts at around 12.6MM. It is just what I prefer. I think one should play with what works for them. Some people have small hands and some have huge hands ect. As far as 13 being the standard it has already been stated that you can always take it down but cannot add. Why is that not logical or rational. When you wear one out just send your cue out and have a new one made to the diameter you want. I feel english has way more to do with the tip and stroke than shaft size.