Thanks for your question. Once you fall outside the 80% range for average GMAT, things get a bit unpredictable. While Harvard and other top programs certainly admit "outliers" every year (applicants with paper qualifications outside their typical range), the odds of getting in drop precipitously. What you may have going for you is your startup non-profit success and your post-MBA vision for work in that area, which will certainly differentiate you from the typical applicant looking to take the for-profit business world by storm after graduation. Emphasize your leadership in your application and try to offer up evidence beyond the GMAT that you will be able to handle a rigorous academic curriculum. As encouragement, I had a client this year with a background in banking and similar goal to work in non-profit, and he received four offers from top ten schools. Remember, it's not only about the GMAT. Your application is considered in its entirety. You are definitely facing an uphill climb, and the odds are not in your favor, but such a scenario rarely discourages true leaders. Good luck.