Making the SAT to IQ leap has to be flawed by the very intent and design of the SAT test. The SAT is designed to predict college performance. Questions, difficulty, etc. are selected to optimize that correlation.

Who most succeeds their freshman year?
I would suggest: The students who come from a culture of education. Students who learned how to study,how to double-check their answers, ones who aren't worried about how they are paying for school, etc. Those who are driven, etc. SAT should be selecting for high drive students with good work habits. It is another reason that some segment of the gifted population (and the higher you go the worse it can be) don't max out, they don't have the drive or past experience to work their hardest.