I took some time to look at research regarding the outcome of high GMAT scores on the MBAs that required them. In fact there is no clearly defined research that I could find, and in a way this is not surprising. GMAT scores dictate the schools you can get entrance to, and so high scores give entrance to better schools, and from thereon in high results become a self fulfilling prophecy.
The highest ranking schools can require scores of 700+, making sure that they only accept the very best students and therefore have the very best graduates. High level business schools will accept around 600+. Average ranking business schools usually require scores of 500 to 550 minimum, and accept most people with higher scores than this.