4.0 unweighted GPA with 1250/1600 SAT will reveal the weakness of the high school program.
In fact, high school reputation is the #1 anchor where GPA and rank are being judged.
Only for state university, the vanilla GPA is important.
Say UT Austin has auto admission policy for top 6%(?) ranked students from ANY TX high school. It makes sense to attend a middle-range high school if your goal is UT Austin, because getting into top 6% at one of the best high schools is VERY HARD - as hard as getting into an ivy.