Re. MIT and admissions: sure, I advise the students I work with to shoot for 800s or high 700s on the SAT Math and SAT Math II and science Subject tests. Of course. However, MIT definitely has some flex for diverse students who score 700+, but don’t hit the 750+ mark.
As I said, my own son, an MIT graduate, got 800s on his Math II and Physics subject tests (actually got his 800 in 8th grade on the Physics test), but MIT really does look at context for URM students (women, ethnic URMs, first gen, etc.) because diversity greatly matters to MIT. They are very upfront about that. They also look at more than test scores. I’ve worked with students who’ve gotten into MIT and students who haven’t, and it has never surprised me to see who gets in and who doesn’t.
My recent response was to someone who was asking about their non-STEM subject tests and my response was, and still is, send it in. A 700+ on a non-STEM subject test shows depth beyond STEM.