<p>Quality is the thing that matters the most. This might be an extreme example but there is a famous Harvard application essay written by a person about his attraction to men which is 2400 words long for a 500 word limit essay and it was so good they had to accept him. But on the other hand if the essay isn't good enough to coverup the extra words it might not be positive to your applications. If the essay is too long there is a chance that the essay has redundent material and the admissions officers might find it boring. These people sometimes read hundreds of essays each day so it is best to keep it short. I asked Princeton about this before I applied early and I got this response:
There is no need to exceed the word limit if possible. One of the things we're looking for in the essay questions is good writing, and part of being a good writer is writing to the limits given to you.
But still it's pretty safe to about 650~700 words so just try trimming yours a little bit. It isn't that hard to cut down 100 words.</p>