I've had a look at both textbooks, to me psych seems to be about rote learning whereas biology is more of a challenge. I did lit 1/2, english and philosophy last year and when exam time came, half of my exams were based around writing essays. T'was slightly a nuisance but I do enjoy philosophy but it is kind of mind boggling sometimes.
Well if I was to do biology(/philosophy), I think i would be very happy with around 40+. For psych, I would possibly aim higher, maybe 42+ ?.
Would you say biology takes a lot of your energy? Because I know the people at my school complain about the amount of work there is to be done for biology, like during their exam they had to hand up a 20 page assignment on the ecosystems or something. :\ And what's worse is my school is completely new so we don't have students from the higher grade to kind of give us guidance on certain subjects.