I would think you are asking about the percentage of test takers. Then according to GMAC (test owner) it is 10%. That's why it is a benchmark - puts you in top 10%. Before I used to think people were raving about >700 just 'cause it's a nice round number
GMAC officially published this information "The number of GMAT exams administered in 2009 hit 267,000, just slightly eclipsing the 264,700 given in 2008." A fair number of those tests were repeats, I don't know exact number though. But to get a ball park figure, do the math. It will be helpful for GMAT prep too