I see this said here frequently, but I would disagree that a student with those stats should apply "mostly DO" based on the stats I see with students applying from my program in aggregate. Perhaps if you're looking at highly competitive states or private programs, perhaps, but for students with strong IS options I consistently have students getting in with lower stats to MD programs.
Is it a good thing to broaden applications to DO programs as well? Sure. But I would not consider a 508/3.7 "low" given strong other application portions (experience, volunteering, etc.).
