Read up on how SAC scores and study scores work. Really. Because no-one can answer this question. With a tough teacher, good questions, a great cohort and good exam performance from everyone, a 60% can get you a 40 or more. With an easy marker, bad questions, a terrible cohort and bad exam performance from everyone, a 99% won't get you a 40.
Basically, you need to look at enough of a range of materials from across the state (including the VCAA assessment materials, definitely, but also work posted on this website, external tutors, textbooks, exam lectures, friends in other schools and in your own, etc) to get a feel for what the *average* quality is and what the average questions are - then you kind of make a judgment about where you think you're sitting. A good teacher or tutor etc can help with making that judgment.
But a SAC score is a result, and a study score is a ranking. So they're totally different measures. Just keep doing your best, and assuming you can always do better.