My teachers have recommended 1400-1700ish words, I think that's around 12 pages. It's not a hard and fast rule obviously but given the depth of EX1 they expect you to write in depth as well, and most of the time this is better achieved with more content. Yes it's quality over quantity but why not more quantity if you can have more quality? Also if we take into account the fact that Eng Adv essays are expected to be 1000 words in 40 mins, then it translates roughly into 1500 words in 1 hr (which is the time you will get in the exam) for EX1.