I decided not to drop one; Biology, Geography, Maths, Chemistry. Its a lot of work; the workload and what you have to do in each subject to understand it does increase quite considerably; the jump from As to A2 is in my opinion a bigger gap than from GCSE to As.
I got AAAB last year and im looking to get AABA this year (im hoping to sacrifice the A in geog for an A in chem), so im able to cope but the workload is more; if you can get similar or better than me and are happy to have a much bigger workload then i would recommend it. However, if i went back i would drop geography (now that i know soton dont accept it); i've already got 70% of the A level though so its a bit late.
I would take 4 for a month of A2 then decide; also, remember to revise the stuff you learn; i've left this till now after going out all the time before christmas and i got into a false sense of how much work it is; im having to work hard now.