“how is the adjustment for most kids when everyone is just as bright or brighter as they are?”
This is the one question where I have some experience (from a different very rigorous school).
The incoming student needs to know that at Chicago (or MIT or a few other similar schools) the workload will be tough, and they will be average. Some students love the challenge and do very well even as an average student. Some students hate it. Some get very stressed out. Some top students would be better off being near the top of their class at a very good university, rather than being in the middle of the class at a highly demanding university.
I think that the most important thing is: The student has to want to do it.