Broad picture-
60% of a candidate's evaluation is based on academics.
1/2 comes from Class rank and the other 1/2 from SAT/ACT scores.
The class rank is weighted with how many students are in your class as well as how many graduates from your school attend 4 -year colleges.
For example - if you go to a very competitive high school ( as determined by your school's profile), your class rank will most likely be adjusted upward.
Why use class rank as opposed to GPA? Because it is fair. You don't want to be compared grade wise with another candidate from another school that is more competitive or less competitive than your school. You are instead compared with the students in your school.
SAT/ACT scores do compare you with students across the nation, but everyone takes the same test and everyone is graded the same.
To add on to what Hawk said - guidance from WP admissions is for students to take the hardest classes that they can take and still make an 'A' or 'B' in.
Candidates really shouldn't compare themselves with one another. There are way too many variables involved. To compare yourself with someone who says they had a 3.0 and 31 ACT doesn't paint the whole picture of that candidate's file. Your file will not be identical to their file. One may have a LOA, one may not. One may be a recruited athlete, one may not. Your nomination situation may be different ( competitive district v not so competitive district, ranked v unranked slate etc,) .
I understand the desire to want to compare but it is really not fair to yourself. You may get incorrectly encouraged or discouraged.
Best advise - do the best that YOU can do.
Sure, get input, ask questions, but in the end, present the best file as possible and be confident that you did your best.
Then - let admissions take it from there.