Lol, yes I've done part of my HSC already, and really, it's not one yearly test. Half your marks come from a number of assessments you do throughout the whole year and the other half comes from the actual external BOS tests. Yes, you have to work quite hard and the workload is significantly larger than in junior years - but also on the other hand, it's much more interesting because you'll be doing subjects you actually want to do. Also, in terms of study - the same amount of coursework that you did in the whole of year 10 is pretty much equal to the amount of work you'll do in the first term of year 11. So to sum it all up, yes the HSC can be hard, but as long as you put effort into it, you should be fine.