dude are u kidding me if anything i would be dropping a subject. You obviously love maths so dont drop uni maths, u'll have a seriously awesome time, If i were you i'd actually DROP biol or Chem. You only need one of them for pre-req, and chem is beta for pre-req than biol, ie it gets you into more.
I actually was down to do legal studies this year and dropped it not 2 weeks ago. BEST DECISION......EVER. so much better for my other subjects.
Bottom line, DO NOT PICK UP PHYSICS, unless you drop biol. and concider dropping a subject (biol) but 8 subjects is crazy and will kill you. Unless of couse ur an absolute freak.
PS: from a more unbised point of view, do physics 1/2 next year and see you you go. both on your 1/2 s and ur 3/4s. if you get 3 49s drop physics. but reli i think its a bad idea to kepp physics.
PPS:Wat school do you go to that is letting you do 3 3/4s in year 11??? (not against ur school or anything, just interested)