Well i can't commnt on IPT cause i don't do it, nor do i know anybody that does, however i can comment on physics ( and chem).
Well physics is more of a mind game for me. Usually if u attempt to visualise a concept, for example when studying projectiles in the first term of year 12 (term 4 of 2004), u juts visualise where a projectile might land and how far it will land from where it was launched..shot ..or wateva, I mean like if u shoot an arrow into the sky, at a 45 degree angle with an initail velocity of 120 km/h, obiously it's gonna go more than 50 metres horizontally, and so when u make mistakes u can easily point them out, by just looking at reality..... I wasn't supposed to be doing physics, however i didn't sneak into the class... because well it was only a class of 2 students and if i tried sneaking in i would've obviously been caught..... however i too had to make a decsion and that was between bio and phys and i didn't decide until like week 8 of term 1 in year 11. But i say do phys, however, could u possibly post up ur other subjects, it could help.
As for chem, well chem is like a whole different world to physics, chemsitry for me is harder and more challenging, however the ammended syllabus has made chem a little more theory than before instead of being 100% actual chemical reactions and stuff... which is why my chem teacher now hates the new HSC (lol)
Judging by SAM, chem is a higher scalar, however i personally think it's much easier to get 90's in physics than chemistry, although i havn't achieved 90 in physics however my final for phys in year 11 was 81% and for chemistry i recieved 71%, so yeh, but hey that's just me, i knwo a few people that feel the same way, and actually dropped chemistry and stayed with physics. But i reckon give physics a try for like 2 weeks, and if u don't like it, then go to IPT, and trust me, if u do decide to drop physics ...if u pick it up....and then feel that u've made a wrong decision, then go back to it and don;t turn around..
On one day i had double chemistry and on that day i decided to drop Chemistry, amusingly i picked it back up the next period because i knew i would regret it (for some reason or another)
In the end it's ur HSC, don;t worry about scaling, pick the subjects ur good at, and as u say ur npot sure what ur beta at (whether it's phys or IPT) then try them both out and then decide. I'm sure u'll be able to catch up on 2 weeks of work.