Graham White was definitely correct in saying that I am not in the running for the top place in 4U or even top 10. I currently maintain a rank about average for Ruse in 4U maths. I am putting all my effort into informatics, not HSC, because I can only do well in tests where the average is less than 50%. I make way to many careless errors to do well in the HSC, and I find the questions boring (I've been spoilt by the interesting Olympiad questions).
Ok, my bets, which I'll only use on 'knowns'
Obviously I'll vote for Graham White, he is the only one on the IMO team, and he is also careful.
Brian and Libling are good bets. Libling is quite strong in Olympiad, making top ten in AMO and APMO and I'll bet for him after Graham. Brian only ranked a few below me in both those comps, so he is quite good.
Yu Heng Lau and Thuc Tran are some good bets for Ruse, they count as 'knowns', especially Yu Heng who used to perform quite well in olympiad before he started concentrating on chem.