if you're aiming for As and A*s, UCAS points will be no factor for you, any university would ask for the letter grades. Would recommend setting it aside on your mind because e.g. ABB and AAC (and especially even more lopsided grade combinations with a mix of very low and very high grades) may well not be viewed the same in admissions despite having the same point value. Universities might impose specific policies on near-misses like not accepting lower than x grade in a certain subject regardless of the others as well, and so on.
Aside from very specific exceptions (Cambridge Natsci, Warwick Maths are the two that come to mind), the only reasons to take 4 A-levels are because you enjoy your fourth subject or you want some insurance for a bad exam. (giving possibly two chances at the third grade in your offer) Fourth A-levels don't really give a direct advantage in admissions since universities are aware that not everyone can do 4. If your fourth subject is too weak to act as a backup (or indeed the wording of your eventual offer excludes this possibility by saying you need to get certain grades in certain subjects) and you don't particularly enjoy it, I would say you can drop it without losing out on anything.