Madasmaths questions have difficulty ratings next to them, the 4-5 star ones are all going to be a lot harder than what you get in the actual exam, 2-3 star is what i would mainly practise with if you're doing normal maths. If you do further then i would advise you do the 4-5 star ones as the further exams seem to be far more about problem solving than most of the old spec past paper questions.