So whats the highest i can possibly get?
C+ is
ALWAYS the state-wide average (median and mode) for any exam, and 30
ALWAYS is the average (again median and mode) study score.
So at the moment, with your C+ midyear, you are about halfway in the total psychology cohort, on track for a score of 30.
The SAC marks are of much less importance in determining your overall study score, but your A is solid so that will definitely help
The distribution of study scores in VCE is such that for a score of 37 (or above) you must be in the top 1/6th of the cohort.
In this Unit 3 exam, 18.5% of people got an A or A+. So at this stage, a low A on the midyear would not even get you to 37, let alone 40. (
http://www.vcaa.vic.edu.au/vce/statistics/2011/midyear/vce_psychology_ga1_11.pdf)
So in theory, if you got a C+ on the Unit 4 exam, you would get ~30 study score.
If you did a perfect exam (no marks dropped), you could maybe push yourself up into about the top 20% of the cohort (assuming that everyone else gets the same marks as they did for the midyear). Top 20% would get a score of about 35 or 36
But don't even worry about any of that:
just go into that exam and do your best to absolutely smash it - that's all you can do