Yeah...98.3 is good enough (still want 99+) - I only need 95 for my preferred course but I might go for MBBS which would be a struggle.
Well, I only estimated a mark to go with your rank, again going by the last two years. I estimated:
English: 86 (probably around this as for 2011, 50-ish got 87)
MX1: 92 (although could be from 90 to 93)
MX2: 82 (probably a bit too low, although your rank isn't helping my estimate go any higher)
Phys: 94
Chem: 89 (you're 5th, so that's borderline 90, I can't see it any higher than 91 going by patterns over the last few years)
So really, you can get into 99+ ATAR if you and your class does well in MX2, but you do need to work on your rank, and go up a couple of ranks in Chem. With English, it's either your grade does well or bombs out (like my year). So yeah, use this as a guide because I reckon it's fairly accurate for your ranks, of course, knowing from experience.