USMLE is one of the main factors in obtaining residency. Also the LOR and clinical grades are a factor. So technically you are correct you can go to any school and do well if the schools teaching is on the same playing field.
Now with that said there are other factors to look at: USMLE first time pass rates will be some indication as to the education of the school, clinical rotation site and even residency placement, as well as if you like the campus and student popoulation.
As far as transfering goes during clinicals I cant speak for any of the other schools but SGU does not allow transfer into their clinicals.
Hope this helped.
SGU SOM Alumni Class '05