This is an interesting question! I think I'd just about manage an A in Maths considering I haven't finished Core 4 yet but got good enough UMS last year to carry me, I'm predicted an A* though. In Further Maths I''d say I'd probably get a low B, failing Mechanics 2 and doing alright in the rest, again I set myself up okay last year, I'm predicted an A. As for Computer Science, I haven't a clue, I'd like to say I'd get an A but probably a B, I'm predicted an A here too.
So I suppose in my opinion these last few months will probably gain me a grade in each subject? Maybe more like a grade and a half where further maths is concerned. But that 1 grade is the difference between getting my offer or not getting my offer, and even then the A* in maths is still a push. So yeah, I'd say these last months of revision are very important.