Unless you are either prodigiously talented or do several quite similar subjects, getting more than three As is going to be a stretch for anyone. Of course it's possible, but not recommended. I really don't think doing Critical Thinking AND General Studies is wise; the window before the exams in which you can take in information having studied it once already and at the same time still recall it when you sit down in the exam hall is brief indeed - unnecessary subjects make it even trickier to work out your schedule.
At AS I got AAAAA because if you look in my signature, all of my subjects were very similar in the exam technique required. The stuff that wasn't duplicated in other subjects (technical stuff in English Language, sciencey bits in Geography) I gave some extra time to, and made it through alright.
I am quite certain that had my range of subjects been broader I would not have been able to produce those grades as easily, if at all.