I suck at essay, but i did about 900 words in the trials (in about 45 mins) and got a 13/15 for my belonging paper and leaving enough time for 40 mins of pre-rehearsed creative time (I do it out of order - ext 1 habit)
I think if my spelling/grammar was better and I answered the Q a little more convincingly I would have got full marks even with only 900 words. I'm not sure about the HSC but I wouldn't think that writing more than 1100 words is necessary. After a certain point your just going to be babbling.
Be succinct, to the point and Stick to the question and you will do fine.
ps, I cannot write more than 1300 words in 40 min of a MEMORIZED essay so don't stress if you think your writing is to slow. its quality over quantity
IMHO you should write 5-6 pages in HSC booklets. which is like 4 regular pages but I could be way off