Hi CJ, each variety is different like you say, and the attachment strength of the stem, color, and firmness all can vary from year to year or tree to tree, branch to branch. My favorite trick with the Etna types like you have there is to give them a slight twist and look at the neck, if wrinkles form it means the skin has begun drying. The figs will not get any sweeter past that point, although if it is hot and dry leaving them will let them dry more and condense the sugars. Wasps will really start going after them once they begin drying though.
Hey Charlie, I poke the stems sometimes when I am feeling unsure, it is not foolproof but most of the time if the small hole does not ooze then the stem won't after being picked either.