I loved psych so much (did it in year 11) and our teacher was very strict on homework so we HAD to do it - there was so much comparatively to other subjects. So interesting though and would recommend it even for interest's sake! I got pretty much the same study score for further & psych, and I did zero homework all year for further, attendance rate was around 50% - it was truly the most boring/painful/easy subject ever. Even if you are good at maths (I found all the maths I did at school to be fairly basic) I wouldn't necessarily recommend further unless you do the work since it's horrible.
Two of my friends did Psych & further, both of them got high 40s in further by doing HEAPS of practice exams and all their homework; also both working pretty hard at psych and one got high 30s the other got mid 40s. They had to put in heaps of hours for psych to get these scores as there was a lot to take in/memorise/learn, and didn't mind doing further work because it was so easy. Note that neither of them are actually that good at maths - one dropped out of methods in year 11, the other got low 30s with actually trying to do reasonably well (tutor, etc.)