Everyone agrees to submit a 1500.
In general, I would differ from some of the above opinions on when to submit. I would submit above 25th percentile (using pre-TO enrolled student score ranges). 75th is far too high a bar in my view.
The MIT thread had some interesting thoughts from an admissions officer. They treated score as a threshold level to show the student was sufficiently capable. Higher than the threshold wasn’t going to help the applicant, as the application review moved on to other factors. (http://talk.qa.collegeconfidential.com/t/mit-reinstates-act-sat-test-requirement/, well worth a read) While other highly-selective schools may well use scores differently than MIT does, it seems to me that a score smack in the middle (let’s say 40th percentile) clearly shows the student would fit academically at a school.