Re: your admissions questions, ask an admissions consultant. We've got a folder here called Ask An Admissions Consultant (or something similar). :)
Next, there is no statistical difference between a 690 and a 700, just a psychological difference (because one starts with a 6 and one with a 7). Seriously - a 690 is a really good score.
If I were you, I would talk to an admissions consultant before deciding whether to take the test again. 690 is on the lower end for the top 5 or 10 schools, but it is on the higher end for many of the top 30 schools, so you may be fine already. You'll also need to give the admissions consultant information about the rest of your profile - school, GPA, work experience, etc. - as the decision does not rest solely on your GMAT score, of course.
Now, if you do decide to re-take, then I'm guessing that most of your improvement will need to come from your verbal score, since your quant score is already quite good. Were you taking your practice tests under 100% official conditions, including essays? What were your subscores (Q and V) on the most recent practice tests?
If you do re-take, then use the below article to analyze your most recent MGMAT CAT:
http://www.manhattangmat.com/blog/index ... ice-tests/Then come back here and post your analysis - we'll help you figure out what to do based on the data!