Yes. It's super easy- a 780 is 90th percentile, and an 800 is 94th percentile.<p>The best thing you really can do are practice tests. Just to warn you though, the Kaplan etc. pre-tests are actually much more difficult than their regular practice tests, and the regular practice tests are more difficult than the regular exam.<p>This way, you will always do better on the actual exam than on the practice tests, and this will make you believe that studying helped, which is actually doesn't.<p>The only accurate measure of how well you'll do are the practice tests given to you by the actual GRE people, and you'll get a disk of those a month or so before your exam, in the mail.
The main thing that you might not have at your fingertips is basic abstract algebra (groups, rings, fields). I'm assuming you know ODE, PDE, linear algebra and other things from an engineering centric education.