My understanding is that, since there is no "hard limit", going 50-60 words over is fine. They don't count words, and have communicated that only really long essays bother them (mostly because they feel the questions can be effectively answered using around 500 words). Beyond that, essays are in danger of wandering beyond the scope of the essay question.
That said, my essays were a good bit over (they averaged about 600 words), which I believe was the right length for the stories and points I included. I may be regretting that on Dec. 17, though.