If you are really hardcore about this, Im going to say
For MX2 and MX1, practise is vital therefore you will need to do more past papers for this, do them regularly.
For Sciences, knowledge is more needed than practise really, the more past papers you do the more repeated questions you get, science long answers are always difficult to perfect, so you will want to spend most of your time on science perfecting your knowledge with extreme rote and consistent note taking, do past papers occasionally in between
For English, doing 100 papers is exposing yourself to 100 different types of questions and stimulus (again things can be repeated), do 50 module ones and 50 Area of Studies. Study your texts as deeply as though its university level, make points for a whole variety of things, people will tell you to rote and write your essays, I am generally against it, but whatever works for you I guess. (I would know my texts insanely well know techniques and stuff, then go into the exam and write what you know)
This is what I would do if I had the self-discipline and perseverance to be able to do this many papers.