I remember when I did VCE, some teachers and a few students were looking into how SACs compare with exams in terms of influence on study score.
I don't think that SACs actually matter too much and your exam performance is the by far the biggest influence on your study score. There's a lot of ways to rig numbers to make them say what you want them to say.
For example, say that you have 50% SACs and 50% exam but the SAC mark median was 97/100 and the exam median was 80/100.
Say you have 5 good students, after SACs, the ranking of these is:
Student 1 -Best
Student 2
Student 3
Student 4
Student 5 -Worst
Now exam performance is reversed.
Student 5: 90/100
Student 4: 85/100
..
Student 1: 70/100
Student 1 ends up with 100% for SACS + 70/100
Student 5 ends up with 95% for SACS + 90/100
Thus, student 5 smashes student 1.
From memory, something similar to this was happening, essentially everyone smashed the SACs after they were adjusted, exams then spread everyone out.
Similar to the Tour de France if you're not great at maths, on the flat stages, there's basically no difference between the first and tenth rider, so you could win all the flat stages and not be very much ahead. In the mountains though, the difference between the first and tenth could be 20 minutes, huge.
Moral of the story is, focus on the exams, they are far more important.