Thanks for posting. To answer your question regarding the GMAT, if you believe you can improve your score by 50 points it will help, although considering your high GMAT score it will not make or break your application. Once you hit a certain GMAT score, which you have, any increase in score becomes increasingly less important.
With regards to your application, your undergraduate GPA is a bit low. You may want to read this case study of a candidate with a low GPA: http://www.stacyblackman.com/comprehens ... ies/case5/
For the schools you have targeted, particularly HBS, I want to emphasize that they are looking to cultivate leaders. I strongly recommend you emphasize your leadership throughout your application.
I have also listed school specific advice here:
Harvard: http://www.stacyblackman.com/comprehens ... ies/case5/
MIT Sloan: http://www.stacyblackman.com/category/mit-sloan-advice/
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