I have taken the GMAT three times last year (1st time: 570 Q-42/ V-27/AWA 5.0, 2nd time: 530 Q-41/V-23/AWA 4.5, 3rd time: 600 Q-44/V-28/AWA 5.0). My goal was to get a score in the upper 600s. I have taken a GMAT prep class and I have studied on my own after the class before taking these. I am debating whether or not to retake it again because I am still not satisfied with a 600. However, I also do not feel that confident that I will be able to make a significant improvement. Even if I improve on my 4th attempt, I don't think my score will be higher than a 640. My average of the practice tests that I have taken is around 640. I am planning to apply for Fall 2010 and I would like to get my applications in by the 1st round for most of the schools that I am considering. At this point, is it worth my time and effort to retake this? Will improving another 20-30 points (if I do) make a significant difference on my acceptance to top schools? Or should I give up and just focus on making sure that the rest of my application is good? Also, if I retake it again and I happened to do worse than my 3rd attempt, would this be looked upon negatively?

The schools that I am considering are: Georgetown, NYU, Cornell, Columbia, Duke, University of Rochester, and Boston University. I am mainly only considering the full-time programs. Ideally, I would like to get into a top 20 program.

Just to give more of my background, I graduated from a top liberal arts college with a 3.35 GPA as a science major. I am an Asian American female and I am working as a financial analyst in the healthcare industry. I have about 5 years of work experience (which includes a promotion and transferring positions) and I am also doing some extracurricular activities. I have also taken accounting and calculus courses after college, which I have done well in.

Thank you in advance.