My teacher advise AT THE VERY MINIMUM 4 pages, and best students write 6+. This is because the examination script book has different line spacing and is very different to a normal lined sheet. You could probably write 100-200 words per page in the examination script book, which is different to the 200-300 words on a normal lined A4 sheet of paper.
I was scared of this too, so I did an entire practise exam in a script book. Got it back today and the rough draft (I just against memorising

) for my context was about 3 and half pages. My handwriting is smallish and piece around the vicinity of 850-950 words
May as well add - my longest piece was I /think/ around 970 words or something, with my shortest being 780 or so I think.
I saw somewhere else he said this was around 5 pages for him?? Correct me if I'm wrong Brendie
It's different for everyone because of their handwriting, I urge you to give it a shot before the exam on Wednesday so you don't panic on the day / waste time counting words. Even writing a page and tonight and counting the number of words will be useful for the exam

(eg I know I write 230-250 per page in the script book so a full 4 pages per essay is a decent amount for me where some people might need 6 or something to fit in the same number of words. I stress that quality is pretty important too though!)
Give it a shot! =)