Here are my 2 cents:
I agree, there is nothing lacking in your application; you are a great candidate for applying to top tier schools, and will get careful consideration at all of them. However, just remember there are more applicants with A averages, 800 or 900+, and good research experience than there are spots at those top schools.
There are very few people that can truly feel confident about getting into any single top tier school. Then there is everyone else who is qualified.
That being said, I wouldn't bet your life on getting into any one school, but I would certainly bet money (with 1:1 odds) that you will be accepted into one (probably more) of your top tier choices based on stats alone.
As for no one knowing what it takes to get in at these top schools, thats true and not true at the same time. Everyone knows you need GPA, test scores, letters of rec, and research experience. What draws the fine line between accepted qualified applicants and rejected? No one knows.
Every school does their application process differently.
In Stanford Applied Physics, as an example, they try to get the best possible students, without worrying much about intended field of study. Then how does it work out that certain labs/areas aren't understaffed? It just magically does.
The process for Stanford Applied Physics is:
Two people read your application in the process, and every committee member has different things they stress when inspecting applications: GPA in certain classes, test scores, research, reqs. You never know who is reading yours.
In the end, I would try not to worry. Though you probably won't get in everywhere (although who knows),
you'll go somewhere real good.