My teacher has marked HSC Papers in the past years and said to study 2 of Skrzynecki's poems in DETAIL. She said it is also best to have 2 stimulus because they may ask for 2 and also have 2 supplementaries. I know its a lot to remember but it is well worth it.
Two or three Szkynecki's, two stimulus and two related material in detail. Do more if you can. Like it's been said, it's better to be overprepared than underprepared.