I'm doing 4 A2s (and a GCSE by distance learning) and it's pretty stressful with all the homework and coursework and exams. I have to say, I'm beginning to regret my decision not to drop one, but I've already applied to uni (and got 3 offers) and I have 3 exams for the subject I'd drop, which is history, in January, so I just have to stick it out. Universities don't ask for 4 A2s, so unless you love all your subject and you don't think carrying on with all 4 will affect your grades, drop one. It is quite nice to have a bit of flexibility though, knowing you can screw up one of your subjects and it won't matter because unis only ask for 3!