I make broth in a crock pot, typically on the "low" setting for 24ish hours. Sometimes this setting is at a rapid boil, sometimes it is at a simmer.
Have there been any studies about the temperature of the broth simmer and mineral/gelatin extraction?
For example, http://www.seriouseats.com/2012/02/how-to-make-tonkotsu-ramen-broth-at-home-recipe.html shows a broth at a rolling boil for 12 hours, and it has the effect of emulsifying the fat into the broth for an extra rich experience. This broth also used pork feet and chicken backs as its main protein and bone components. (BTW this was Amazing, and is slowly becoming my broth of choice.)
Then, you have the WAPF endorsed method of a slow simmer, and suggests that boiling will break down the collagen and gelatin. http://www.thehealthyhomeeconomist.com/video-the-perfect-simmer-on-your-stock/ This method is also endorsed by most French trained chefs, that insist on having a completely clear broth.
Do you monitor the temperature of your broth, and/or do you care about how clear or cloudy it becomes?