I don't do VCE so my knowledge of it may be limited.
However, I do know that different schools have different sacs with varying difficulties. There is no way for me or anyone else on this forum to know how difficult they are.
However, if you do well on your exam then it makes your sacs scale up and therefore you will get a good study score. A 35 SS is 100% achievable with a good exam score.
Your exam is the most important assessment item; your sacs don't matter nearly as much. Don't stress over them.
P.S. Sac RANK is the only thing that matters. VCAA only looks at rank, they don't directly look at your raw percentage.