Overhead press is a much more accurate measurement of upperbody strength than the bench press even when you are standing and need to push forward close grip inclined bench is the nr 1 exercise and actually Charles Poliquin uses this exercise to determine how good an athlete on upperbody pressing strength.
About overhead squats i'll just say is only after you get past the flexibilty issues and start working on some serious strength that you will be able to understand it. Someone who gets to handle heavy weight on overhead squats gets to have fully functional pressing strength and a core of steel.