I have never seen a piece that only has two pages or less (handwritten) receive a score above 7.
All the sample "high scoring" essays I've seen on the internet and the ones my teacher has given us written by past and current students all have around 3 pages of writing.
We're getting too bogged down with irrelevant technicalities. You can't really measure the quality of the piece with quantity of pages, for obvious reasons I won't bother explaining. But if you must know, my English teacher (yes, he use to be an examiner) gave my class a two page sample essay (the handwriting was quite large) and scored the student a 25/30.
OP, page numbers are irrelevant. When you're writing an essay, the first thing that pops into your head shouldn't be "oh okay, I've got to write at least 3 pages and then I'm set," you should be focusing on divulging your ideas and presenting them in best possible way.
There is no number of pages that needs to be satisfied to produce a high scoring essay because I believe that sometimes the key to writing a great essay is brevity.