Hey! I didn't do eng lang but I did 3/4 Lit, so hopefully I can give you some insights into the lit side of things.
Lit is definitely a difficult subject as it is very different from mainstream English and the sort of assessments you do in lit are also very different from the assessments you would've done from year 7 to year 10 - but I would say that is the main reason behind its difficulty. For lit assessments, in unit 3 you will do a creative piece and an essay comparing between a text and an adaptation of the text (eg. a book + a film). In unit 4, the two assessments are literary perspectives and close passage analysis. Most students find Lit Perspectives to be incredibly challenging as it's actually more on the edge of the sort of assessments lit majors do in uni. Close analysis can also throw some people off at first as the structure is very different to the usual english essay. Finally for the exam, it's two essays (one literary perspectives, one close passage analysis).
I would say that lit is actually pretty easy to score well in if you understand the criteria well. The reason most people find it hard is that most people who choose lit are those who previously cruised through year 7-10 English. Then they go into lit and write the same sort of essays they've been writing for the past 4 years, only to get mediocre scores because they don't realise the criteria is completely different. So if you are able to grasp the differences between english and lit and write according to the actual criteria, you're pretty much set for a good score.
I hope this gives you a bit more context in terms of what to expect if you do lit! If you have any more questions, feel free to ask. Lit was definitely an incredibly challenging subject for me but it was also super rewarding and it definitely gave me a different outlook on a lot of texts I've read before.
ETA - you mentioned that you're aiming for a high ATAR. Many people choose 2 English subjects to try and maximise their ATAR since an English subject must be in your top 4.