If you want to get a grade 6 in gcse maths, you’ll have to take the higher paper. The highest grade you can get in a foundation paper is 5. In higher, you need less marks to get a grade 5, however the questions are harder. Vice-versa for foundation. If you’re worried about the amount of marks you need, then perhaps you should take higher which requires less marks but you’ll have to revise harder to answer those harder questions