Those results are beyond amazing, I've just finished AS and did pretty well, but didn't get GCSE results as good as that. GCSEs don't determine everything, but honestly with those grades its clear you have the capability of doing 5. People at my school who did 5 found the workload to be fine, and remember further maths is just doing additional, slightly harder maths so shouldn't affect other subjects too much, but others may disagree or have different experiences. Can't speak on behalf of English, but I found Biology and Chemistry a moderate workload IMP. You could always try Further and then if it's too much work, or you're not enjoying it, just drop it, no harm done. Also, having Further Maths would be an advantage when it comes to applying to medicine, especially at top Unis. But, it's your choice if you don't think its a good idea or you don't want to do it, don't bother. Just don't let others completely persuade you into doing it or not, take advice and make your own decision. Hope I could help