I did not know it existed till you asked. My school offers Statistics but not further maths so never heard of it before, also you don't really need the extra GCSE for any A level or University course. All Universities would only want GCSE Maths at A*-C and your better of just doing Maths than putting extra pressure on yourself. It would be better to get an A* in Maths than get something like a B due to the further maths pressure. I see you are bright and intelligent but, really is it worth the effort? do you actually need it?