My DS is in a PhD program at Caltech, and he did mention that grad students there do tend to hang out with others in the same program.
He chose CT because it was the highest ranked grad program.
I suggest you contact some of the current grad students to get direct input from them- a word of caution, CT is on break this week so you may not get immediate responses.
http://www.bsn.caltech.edu/people/gradstudents.html
Congratulations on great acceptances!