What you are asking is, in my opinion, very hard to answer. Bear in mind that at the PhD level, it is more than just your GMAT or GRE that determines whether you get in. Heck i can give you anecdotal evidence in the form of people i know who have 700+ GMAT scores and still didn't get in.
At hte PhD level, you are up against a whole host of smart people with high scores. I believe schools look at more qualitative factors outside of the standardised test scores. Schools like Harvard or Princeton are used to seeing amazing test scores> I believe those who get in got in throught the stregnth of other parts of their application, such as LORs and SOPs, APART from their test scores.