Which Ivy League universities look at both internals (School exams) as well as externals? (Cambridge exams) Also, which IL Unis look only at externals? (CIE specifically)?
Interns and Externals matter for all.
The main academic documents the Ivies look at are your school report grades (mid year and end of year) for the last 4 years of high school and your GPA. Since your mid-year school report is probably determined by your internals and your GPA is the Grade Point Average of ALL your grades, both matters.