I've been taking GMAT practice tests on my own, and am consistently scoring between 640 and 660. I think that my other qualifications (GPA, writing and interview skills) can put me in the running for top-tier schools, but their median GMAT scores are listed higher. I'm wondering whether to go ahead and take the GMAT now, or if I should take a course and try to raise my score?

Suggestions? :)