hi there!
regarding your school sacs, it can be hard to predict what grades will help you achieve a 40+ study score. this is because your final letter grades for GA1 (unit 3 average) and GA2 (unit 4 average) are influenced by factors such as the difficulty of your sacs, your ranking in your cohort, your performance on the final exam, your cohort's performance on the final exam, and etc..
ultimately, it is your exam performance that really matters. usually for a 40+ score you should aim for an A+ (or relatively close to it) on the final exam. if you look at the graded distribution for psychology from previous years you can estimate how many marks you need for an A+.
and yes, i would argue that psychology is somewhat similar to further, in that both subjects are quite popular/competitive and involve content that is deemed to be 'easier'. this doesn't necessarily mean the examiners care about how much you get wrong, it's more so since the subject may not be as difficult, more students have the opportunity to do well. therefore, this means losing just a few marks can be more detrimental to your score compared to other subjects, as majority of vce works by some kind of ranking system.
overall, psych is a great subject and can be very rewarding so long as you stay of top of the content and practise answering questions! good luck!