I turned the ranking thing into a competition with my best friend. We were both doing really well in chem, our assesment marks were like 0.5% different. In the end, he ended up coming first and by 1%. But we got the exact same mark in the hsc exam itself, but he ended up with 93 while i got 92...
I didn't really learn any of the theory until a couple of days before the hsc, there was way too much to remember. I pretty much bullshitted my answers in a sophisticated way and wrote good algorithms. I was lucky and got a decent test compared to the previous ones.:)
I did software and 4 unit maths. Software isn't particularly easy (in fact quite hard), but without natural computer/programming skills, you will find that it will take a lot of time. Also, 4 unit maths didn't take too much of my time, I just did lessons in the morning and topic hsc questions...
But 4unit can't possibly boost the scaled 2unit mark any higher, it may help with 3unit, but i wouldn't recommend sitting the 4unit hsc this year. 4 Extra marks in 3u (which would be very hard to get) will only get u about 0.4 more uai points.
Thats no reason to repeat, 48/50 is an awesome mark, keep it, spend time on your other subjects. Another 4-5 marks won't boost your UAI too much higher. Also, if you get an easier hsc exam in 2009, you would have to work twice as hard to get that mark.
Also, why are you going to do 4unit maths...