I can only really answer for Advanced English and modern history, but English is pretty much a standard subject– you don't have to spend too much time but just get through the material and form your own insights (and write fast, lol) and express them articulately and argue all your points with techniques and stuff. Scaling wise its obviously much better than standard, and just slightly lower than extension 1 (in fact, many people say how the workload for 3u English makes the scaling pretty irrelevant haha).
Modern history, I dropped in year 11 and for good reason too LOL. History itself is really interesting and personally I'm really passionate about reading up Wikipedia articles on random historical stuff, but you don't usually get to choose your electives, so if you have a 'boring' elective or poor teacher who prefers to give you a heap of readings and not actually any insights/discussion, its really dry. It scales pretty well, the second highest scaling humanity after eco, but the content is actually crazy. You also can't usually just get away with memorising essays, you have to fully know everything and yeah content is massive. I'd suggest finding out what electives your school does for prelim and hsc, and if they appeal to you, it may well be worth it!
Regarding scaling, I'd say do the subjects that scale 'well' by all means but never sacrifice 'scaling' for interest. By year 12, your interest (and hence your effort) will only remain if you enjoy what you do. So like don't do physics for the scaling even though you're really good at extension English and passionate about it too!
