Not sure about all the subjects, but generally speaking it's not really possible to equate raw SAC scores into study scores simply because at different schools we have different levels of difficulty. e.g. At one school, students might average 40%, but another they might average 80% but in the end the SAC scores get moderated depending on the cohorts exam score.
You can view the 2017 VCAA Grade Distributions here
https://www.vcaa.vic.edu.au/Pages/vce/statistics/2017/statssect3.aspx#H3N10065(It basically shows you where the cutoffs for the various grades were e.g. a 95/120 would have attained an A+ in Biology and the general rule of thumb I believe is that all low A+'s = 40. Of course, that depends on where you lie within the A+'s e.g. if you had a really high A+ for the exam and mid A's for SACs that could still be 40+)