How many synths in your opinion would it take to convince you that you are 99.9% sure that you
are at cap and wasting time continue with the same synth?
First, if it's a main-craft synth, and you're not sure the wiki is right (or if it doesn't have the level yet), the first thing you should do is check the recipes at the guild NPC that gives you a list. If you are able to see the recipe in the list, then you are at or above the cap for that item. It's also worth mentioning that you can check the cap by attempting the synth on a char with lower skill (15 levels under cap can attempt, 16 cannot).
For the handful of recipes that do not appear in the list, and for sub-craft recipes, this is purely a mathematical question with one unknown: chance to skill up on a given synth. If you estimate the chance to skill up at around 25%, then the probability of doing one synth without a skillup (if you are indeed under the cap) is 75%. The chance of doing two without a skillup is 56.25%. Three: 42.19%. Etc. Keep calculating, and you'll find that 24 synths without a skillup is just a hair more than a 0.1% chance, meaning you are just less than 99.9% sure. Doing a 25th synth actually puts you past the threshold.
If you lower your estimate of chance to skill up, to say... 10%, then 25 synths only makes you 92.8% sure. You need 66 synths to be more than 99.9% sure.
Artisan's advantage doesn't figure into it. Edited, Apr 4th 2012 10:43am by VxSote