For every person on this forum demonstrating concern for his/her 990, there are two reasons for such a seemingly unwarranted fit of paranoia. Either the person is genuinely concerned, and thus lacks the common sense and intuition that I would assume any talented physics major should have, or the person is trying to find some shameless way to showboat around.
Either way, 99th percentile means exactly what it sounds like, as in you are in the top 1% for a standardized physics test. For the purposes of the Physics GRE, the "talent resolution" is certainly not below the single percentage range, so of course admissions committees won't be able to discriminate between 990s--you have to realize they're going to look at your score, see that it's above some threshold (so they don't have to throw your application out), see that its a *generally* high score (and possibly bump you to the top of the stack of applications into which they'll delve to look at everything else, like letters of rec, statement of purpose, GPA and curriculum, etc), and then never consider your grade again. The GRE is just a rough filter, nothing more. This concern for fine details would be much better directed toward things like your statement of purpose, not to mention the quickly approaching deadlines for submission.
Singularity, perhaps you weren't trying to showboat, and I apologize for the rant, but there have been many other instances of other individuals trying to find some (in their mind) subtle way to illuminate their top score by feigning concern for it, where as common sense should dictate that they should be the LEAST concerned out of the entire 100% of the test-taker pool, and more concerned about other aspects of their applications. I'm not bitter, I did very well too, but I do believe modesty is a virtue, and I know that parading around the 990 with some extraordinarily unjustified concern is just going to make those who didn't score as high as you (the other 99%) even more worried, perhaps MUCH more worried than they genuinely should be. So even if this wasn't your intention, I know there are a few others just itching to let everyone else know how well they did, and if that happens to be the case, do the honorable thing and just post on the grad school topic where everyone's listing their stats and grad programs.
And congrats, btw, best of luck in the admissions process.