When I was just beginning my playing, I wanted a new cue. I decided to research the specifications of the cues the pros used. My thinking was that that if I got the same, then that would be a good step in the right direction...
As it turned out, the pros cues are all over the board so far as the specifications go! They were just as different and varied as the players cues in my local area!
With weight I did notice that 19.5 oz seemed to be common, but they were still all over the place with this. I think some were 17 to 21 oz.
So far as shaft size at tip, if they are using a Predator shaft which uses a dime shaped tip, then 12.75 mm is about as big as you can get. The curve of the dime shape will come down to the edges of the ferrule. So if larger shaft size than 12.75, you will not be able to reshape your tip many times.
With my own experimenting I found that a larger shaft is better (for myself). I had problems when trying a 10 or 11 mm shaft. 13 or thereabouts was better.
BUT I also found that a dime shaped tip worked best for me. So therefore I want the largest shaft size I can get while using a dime shaped tip. And this is 12.75 mm.
Then lo and behold, I later bought a Predator low deflection shaft and it came with a dime shaped tip and was 12.75 mm shaft size at tip!
So I have a dime shaped tip, 12.75 mm shaft size at tip, and 19.5 oz weight. Took me quite awhile to adjust to using this when switching from a 13 mm shaft and a nickel shaped tip though. About a year as I recall.