Prelim Physics is more interesting than Prelim Chemistry (although Prelim Chemistry is just as easy and nearly as interesting)
Prelim chemistry and prelim physics are roughly the same difficulty
I found HSC Chemistry easier and more interesting than HSC Physics (except I did like the Space topic in HSC physics)
HSC physics is harder than HSC chemistry which is harder than HSC biology (that's why biology course has lots more content to compensate and similar story for chemistry). HSC Science is sometimes a bit of a joke, because in the course, there are things that are technically not correct scientifically (e.g. some of the cathode ray conclusions)
Plus real science also includes a bit of calculus (which I think the pre-2001 course did - I could be wrong).
Then again I did the Industrial Chemistry option, which is fairly similar to the ammonia section in Chemical Monitoring, which means more cross-over.