I (and probably a few of the other commentators) get a real sense of deja vu here.
The ideal length of a Band 6 essay is "as long as you need to prove your points". I wrote half of what anyone else in my cohort wrote and consistently beat or equalled all of them. That's 18's and 19's against some of the "best" students in NSW, with 4 or less booklet-pages on average.
Rather than getting hung up on word-count, you should seek to improve how you write under timed conditions. Write as much as you can in 40 minutes; if you find yourself unable to comprehensively provide a strong thesis, points, and evidence, identify what you didn't get done and where you could do better (e.g. spending too much time on the introduction, or forgetting valuable quotes/techniques while trying to back up a point). Then fix them, and try again. And again. And again.
You won't get to count how many words you write in your exam, so why bother in your practice?
I would recommend at least 1000 words for each, but it is not fixed in stone, quality will always be more important than quantity. Just make sure you answer the question and nothing but the question if you want to get the marks
This girl she give good advice (despite what I said above, you typically need at least a certain amount to get your points proven. My "lower limit" would probably be about 800/3 pages, but you have to be SHARP to do this well. And you can, with practice).