My HSC subjects are Advanced English, MX1, MX2, Chemistry, Physics and Economics (i.e. 12 units in total).
Extension 2 Mathematics is great. It's fun. It's eye opening (the first topic essentially teaches you that you know pretty much nothing about mathematics). And it's my favourite subject. It's challenging and of course will require a high amount of work from you (MX2 can take up 30% - 60% of a person's time and effort), but I feel that people tend to exaggerate both the difficulty and workload of MX2. MX2 is perhaps the most fast-paced and dense course offered by the HSC. I personally found it enjoyable and it didn't seem to get in the way of my other 10 units. In my sense of fun, Extension 2 maths is as fun as you can get; there is very little to no rote learning, you have to improvise and think creatively, critically and logically, and the last questions of exams can get extremely difficult, but you are always fully engaged with them. It's a break from the significant amount of rote learning in most other subjects. My HSC is in less than 2 weeks, and I'm only putting in 12 hours of work into MX2 a week (which is about 20-25% of my study time each week). You won't regret doing Extension 2 Mathematics. Fascinating, challenging, highly rewarding and truly will provide you an appreciation for both the power and beauty of mathematics.
I've always been someone who isn't particularly keen on English, and typically scored about 70% in exams throughout my junior years. Up until this year, my HSC year, where I suddenly finished with an internal raw result of 90%. English is often a love it or hate it subject. My god, I love all of my HSC prescribed text: King Richard III and Looking for Richard, the poetry of T.S. Eliot (WOW), and The Art of Travel (a highly engaging non-fiction book, which one may find from time to time exclaiming to oneself the brilliance of the language). The only text I loathed is my discovery text, Wrack, which was a wrack. While I enjoyed the content of English, I didn't quite enjoy the assessments. The essays require a very specific type of writing style which you really need to be skilled at in order to excel in English, and the creative piece feels too artificial and contrived to feel much pride as a composition of one's own. The key to doing well in English is in reading and understanding the syllabus and what it demands of you, which the vast majority of students across the state ignore. I personally enjoy essay writing, but the amount of preparation a lot of students do for English is among the main reasons why they don't enjoy the subject. (Also, I liked to add that I personally enjoyed and performed better in HSC English far more than Preliminary English.)
I had high expectations for Physics when I chose it back in Year 10 (wow... that's two years ago). Some aspects of the expectations are met, but others, I was a bit disappointed by. The mathematics within Physics are mostly computational, and you are taught to use the formulae provided, rather than understanding them (and hence at times, you'll just be playing around meaninglessly with formulae until you reach the answer). One of the biggest flaws in the Physics course is the rote learning aspect of it; there is a significant historical aspect of physics which unfortunately involves quite a bit of rote learning, which only worsens in the HSC. In terms of the overall difficulty and workload of the subject, well... I had a very lenient Physics teacher who never sets any homework and actually assigns certain lessons to do calculation practices, hence I didn't do much apart from regularly keeping up with my own revision notes, and the past papers prior to exams. I feel that doing academically well in the subject isn't difficult, but at times, the content can be challenging to understand (to the point where many students simply accept the theory, and rote learn responses, and teachers often fail at explaining the content and recommend you to prepare responses and keywords). However, Physics is a very intriguing subject. The preliminary course was decent, and similar to how MX2 teaches that you know nothing about mathematics, HSC Physics teaches that you know nothing about the world. (e.g. relativity, the particle theory of light, the idea of quantisation). Physics can be a very mind-blowing subject at times, which defines my appreciation for it
Chemistry is one of the more practical science subjects. While Physics focuses more on the theory, Chemistry tends to converge on the practical aspects of atomic knowledge. It's quite a popular subject, and among the favourite of a lot of my peers. While Chemistry has less rote learning in exam responses than Physics, there's a far greater aspect of specificity and memorisation (e.g. solubility rules, testing for ions and compounds, the formulae of certain compounds, steps of experiments, exceptions, et cetera). Chemistry can be a very fascinating subject despite its convergence upon practicality; e.g. the idea that when you dissolve sugar in water, it reaches an equilibrium where the sugar is simultaneously precipitating out of the solution while dissolving into it at the same rate. Regarding workload, I personally find that the workload for Chemistry is somewhat more than that of Physics, and my revision notes for HSC Chemistry succeeded my HSC Physics notes in length. Overall, I think that the sciences aren't that difficult in terms of workload, and I think you should cope it with perfectly fine, especially if you have a fascination or appreciation of the sciences, then it honestly doesn't feel like work.
Since I didn't do Japanese, I can't comment much on it. However, a good friend of mine does Continuers and Extension. For my friend at least, it seems like that there is quite a significant workload for Japanese; during lessons I have with him, including MX2 lessons, he would spontaneously take out his personal notepad for Japanese and start memorising phrases and whatnot. He actually has an app on his phone which he uses to test each individual word. From what I've seen, at school at least, he seems spend just as much time (or more) on Japanese than MX2 (and he also does Standard English and Chemistry, which the latter being his absolute favourite). With any language subject, Japanese is perhaps centralised upon rote learning. He seems to enjoy Japanese, but the language subjects are hardwork.
From the people who do English Extension 1, they say that it's more enjoyable than Advanced English and more individualistic. However the topics are a love-or-hate. The impressions from people who do Legal Studies say that it has a fairly significant but manageable workload. My friends who do Modern History don't talk about it, so in a way, that's saying something.
Now scaling:
-MX2 scales insanely high: bottom 25% of the state (e.g. a raw mark of about 45/100) receives an ATAR equivalence of 98.
- Advanced English, contrary to what a lot of people believe, scales quite well, especially since it's not a particularly easy subject, and hence not very difficult to get ahead of the cluster of students across the state. A raw mark of about the 85 (top 10%) is enough for a Band 6, and an ATAR equivalence of 97. (It may not look as great because it's juxtaposed against the ridiculous scaling of MX2, but it's better than a lot of the social sciences.)
- Chemistry is the highest scaling science subjects. A mid 70s raw mark (top 10%) is enough to get you a Band 6 and an ATAR equivalence of 98. The interesting thing with Chemistry is that it scales high despite low marks: getting a raw mark of 58%~, which is top 32% of the state, is enough to get an an ATAR equivalence of 90.
- Physics scales pretty good also; a mid-lower 80s raw mark is enough for a Band 6 and an ATAR equivalence of 98.
- For Japanese Continuers, you need approximately a raw mark in the mid-80s for a Band 6 and an ATAR equivalence of 95.
- Japanese Extension scales significantly higher than Japanese Continuers, but I don't have enough statistics to give you a Band 6 raw mark approximation, but you can probably assume it's lower than Japanese Continuers (high 70s perhaps).
Enjoy your Preliminaries and HSC!