SAC scores are not a good indicator in my opinion. The difficulty of the SACs vary from school to school and therefore it isn't a standardised figure that can give you an accurate idea of where you would be ranked in the state. Nevertheless, aim for a perfect SAC average. Don't be overwhelmed if you drop a couple of marks now and then.
The exam however, is a level playing field. Everyone in the state is sitting the same paper. Aim to score 60+/65 marks in the exam if you're looking at 45+. Anything lower decreases your chances because the subject itself is not very difficult and because of that, there will be a bunch of kids sitting at around the 55/65 mark.
As with any subject, business is very competitive as you near the high 40's. Most of the time it is the exam what separates a 48 from a 50, not SACs.