Ultimately, it is about what you get for O level: your L1R5 and
your L1R4.
Do not take a subject combination just because you want to go to
a particular class or because you want face. Anyway, you will only
have the "face" for at most two years, because after that, everyone
will be looking at what course you take in poly or which JC you go
to.\
If your grades are only borderline (below 65%/70%) and you
squeeze yourself into top class, firstly you will be among the last
in that class. Secondly, which is more important, you may not cope
well with the subject.
Suggestion:
I am sure at some corner of your school there is this
noticeboard with all the examination results of national
examinations. At my school, there is such a noticeboard outside the
general office.
Go there. Look at the examination results for O level. Look at
the passing rates and distinction rates of the O level
subjects.