I’ve been doing some research on this and here are the guidelines I was looking for. Just in case someone else comes across this thread with the same question. Having said that the advice I got here,“make notes of what you do and learn from experience” is the next step from this starting point, I am sure.
These are my notes from “Sous Vide Cooking a Review” By Douglas Baldwin.
Available here: https://www.sciencedirect.com/science/article/pii/S1878450X11000035
At sous vide cooking temperatures between 55C and 60 C, many of the enzymes have been denatured but some of the collagens are active and can significantly increase tenderness after about 6 hours (Tornberg, 2005)
Collagen fibres start shrinking around 60 C but contract more intensely 65C Shrinking mostly destroys this triple-stranded helix structure, transforming it into random coils that are soluble in water and are called gelatin.
Muscles used for pulling the legs backwards have a higher level of elastin which does not break down with temperature. So toughness will not reduce with cooking.
In general, the tenderness of meat increases from 50C to 65C/ but then decreases up to 80C (Powell et al., 2000; Tornberg, 2005).
At 80C/176F, Davey et al. (1976) found that these effects occur within about 12–24 hours with tenderness increasing only slightly when cooked for 50 to 100 hours.
At lower temperatures (50C/120F to 65C/150F), Bouton and Harris (1981) found that tough cuts of beef (from animals 0–4 years old) were the most tender when cooked to between 55C/131F and 60C/140F. Cooking the beef for 24 hours at these temperatures significantly increased its tenderness (with shear forces decreasing 26%–72% compared to 1 hour of cooking). This tenderizing is caused by weakening of connective tissue and proteolytic enzymes decreasing myofibrillar tensile strength. Indeed, collagen begins to dissolve into gelatin above about 55F/131F. Moreover, the sarcoplasmic protein enzyme collagenase remains active below 60C/ 140F and can significantly tenderize the meat if held for more than 6 hours (Tornberg, 2005)
For example, tough cuts of meat, like beef chuck and pork shoulder, take 10–12 hours at 80C/175F or 1–2 days at 55–60C/130–140F to become fork-tender.
Intermediate cuts of meat, like beef sirloin, only needs 6–8 hours at 55–60C/130–
140F to become fork-tender because the tenderization from the enzyme collagenase
I also found http://www.cookingissues.com/index.html%3Fp=3911.html to be helpful.
I hope it is of use to someone.