I agree with porscheboy.
I like to think of the opportunities at and after bschool similar to the reputation, quality etc of the program as your GMAT score.
Sounds funny?read on.
If you do well initially (good grades, network, career research), you can get a great score(career success).
If you start small (small, lesser known program), its really difficult to catch up in the later stages.
And then we know that the GMAT is one part of the application . Depending on the business school and your circumstances, it may play havoc on your plans or not count for much. (Translate this to high strung careers in banking, consulting which are difficult for grads of lower ranked schools to secure)