Hmmm... I did pretty well in the exam, obviously (though probably not perfectly, I reckon I dropped some marks in the language analysis section). But my SAC marks weren't perfect. We did six SACs for english; I got A+ in four of them, and A in two of them (interestingly enough, those two were the essays on the texts that I did in the exam. Strange...). Even my A+s weren't perfect; I think I got full marks in one or two of them, but the other two were only just A+. And the rest of my year level were similar; only three people got A+ for every SAC. I was ranked somewhere in the top ten for English, but probably not the top 5. And yet, at the end of the year, four people from my school got 50 in English.
Moral of the story: you can get 50 for the course even if you don't blitz the SACs. On the other hand, you obviously have to do reasonably well in the SACs. And you pretty much have no chance of getting 50 if you don't get at least 58/60 on the exam.