are you aware of this site?: http://www.gradschoolshopper.com
this is data collected by the AIP. many schools list the average GPA and test scores of their admitted applicants. You should take a look at these for various schools and see how the trends go. Then take a look at the applicant profile and admission results thread we have in the grad school forum. Also, many schools publish statistics about their incoming physics class, you just have to look around on the physics department websites. This sort of thing takes a lot of research--I know because I spent an entire summer doing it.
For top 10 universities, you should have a GRE at least above 900 and lots of good research experience.
If you will not have research experience by the time you apply and you score above a 900 but less than a 950, I would look at schools ranked 20-10, maybe pick one top 10 school that you really like, and a few backup schools in the top 30/40