I have a Predator Z2 shaft, another cue with an 11.2mm shaft, one with a 12.5mm shaft, one with a 12.75mm shaft, and one with a 13mm shaft.
Personally, the smaller the shaft the more I hate it. Unless you have a perfect stroke (and I certaintly don't), IMHO, it is easier to miss shots, especially long straight in shots.
I tried a 14mm shaft and it was very accurate for the long shots without much English. It I didn't have small hands, I probably would use one.
My ideal overall favorite shaft is 12.75 because it can put plenty of English on the cue ball and it is fairly easy to use for the long shots. I like the Predator evenly tapered shaft, but I can stand the feel of the hit you get. So I am going to an OB1 shaft, even though it has a taper to it.
To summarize, a lot depends on your style of play, and what game you are playing. For me, I rarely go beyond one tip from the center. That is why I use a 'dime' rounded tip, to avoid miscues when I do use a lot of English.
In 1968, when I bought my first Josh cue, everyone recommend that I get 2 shafts - one for 9 ball (12.5mm)and one for straight pool (13mm). I ended up playing more with the 13mm. You may consider this route, buying one than one diameter shaft.
Hope this helps.
Thanks.[/QUOTE]