Wow that is quite a high percentage to cover for a year 10 student.
personally, I would say leave past papers for year 11 because otherwise you will exhaust your resources and you won't have anything new left to do in year 11.
secondly, you need to bear in mind that although 85% sounds beautiful to cover, is it realistic?
I did Latin for GCSE too. Although it was tough to revise for, the outcome was totally worth it. You need to know your vocab and tenses inside out until you can recite it in your sleep. Practice translations even if you're not completely comfortable with the grammar, it'll show you what you need to go back to read over again.
What text are you doing for literature?