ask your teacher, who (hopefully) is experienced and knows what sort of marks it takes to go well in 4 unit, and whether it is worth your while doing it.
But if theyre raw marks of 60 in an exam that's not exceptionally easy, I think you'd be looking at about a band 5 - potentially more if you work harder or if you're doing really hard exams.
in the hsc, i reckon i only got a raw mark of around 60% judging from the number of questions i didnt finish, and i got 88 as my final mark