well there's really nothing that I can say that hasn't been said already, but I'd say there's really not much difference between a 49 and a 50, down to luck I guess.
I was allowed to acclerate in my two subjects because apparently I had "natural ability" or "affinity" for maths and sciences. Personally I put that down to work ethics (aka i just did the work that was set) but I always had a tendency to remember things faster which helps in less mathsey subjects like physics

This brings me back to my first point I guess, since I actually tried a LOT harder in methods than physics. Ultimately, when I got my statement of marks (that i applied for) I saw I had made wayy to many silly mistakes like on simple domain/range qs so I was "unlucky". I reckon I'm just careless, which is why I dropped out of further haha. So being meticulous and careful is important too, if you're aiming for that high score.
As for physics, I spent less time on it and I was rather lucky that I did well on the two exams which boosted my relatively low sac marks.
On the other end of the spectrum, one of my friends COMPLETELY aced all her economics sac was completely shattered when she only got in the mid 30s.. she hadn't lost a single mark in her sacs. What had happened was she, and a portion of the rest of the state, had mis-interpreted a 6mark question... back luck(?)
Finally, to round off a nice and long post (I have way too many frees at school =w=) my 'answer' to your personality question. Umm, pretty much I'm determined. This one competition q took me nearly a whole year to work out but i finally got there! I also prefer working alone, read textbooks by myself rather than be taught the same thing in class and i guess to an extent, rather humble.
There are others in my cohort that excelled and got 47-50s and they all have very good work ethics, sometimes staying back hours after school. While im usually all over the place, some people are really organised which helps in getting work done on time and gives structure to your day.
Oh, and this probably has nothing to do with your post, but I sleep a lot. Like, 9:30pm(or earlier) - 7:30am. I live close to school, ~10min walk so I used to go for a morning run (got lazy, not anymore) but I found that good sleeping patterns and exercising regularly helps study patterns. I'm usually the only one awake for indo school on saturday morning haha, which means I can learn in the morning

Some people do sleep late but they.. well.. I'll leave at they always seem tired at school and its a bit hard to learn if your in sleep-deprived zombie mode

GOOD LUCK =D