Well the major premise of IB is that you must learn the exact contents for a huge two week session of exams at the end of two years, so it definitely helps if you can reproduce your knowledge confidently in the context of an exam paper - on the other hand in the US I don't think that anybody really seems to be too bothered by the score you get at the end of the two years and your teachers ignore the IB and just continue handing out grades based on your homework, tiny in-class tests and how crazily enthusiastic you seem, like in any normal american course. So not being able to perform in exams may actually not be so bad for you as US universities don't seem to mind so much about your final IB score, provided your teachers like you.
To my understanding, pre-IB is one or two years before the actual IB where they try and give you the groundwork knowledge which will enable you to be okay in the actual IB. On that basis, you can always opt out of it later if it's not suiting your tastes - so in my opinion you should give it a go
It's not like you're committing to do the actual IB. Most countries have no such thing as pre-IB so it's just kind-of something some schools invent for themselves to make sure students aren't behind when they come to the actual Diploma. Trying it out might help you make up your mind - and I don't know what honours classes are exactly but they sound like they should be impressive, so if you're smart then pre-IB might be more interesting/challenging for you... who knows
Can't know how something is until you try it, and this pre-IB thing sounds like a year where you can give it a go with no strings attached.