Re: #17 and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3090148/
They found that SAT correlation with GPA for “high ability” (mean SAT 1158, mean GPA 3.17) subjects was 0.35, versus 0.19 for “low ability” (mean SAT 921, mean GPA 2.87) subjects.
HS GPA in various other studies tends to show higher correlations than 0.35 and/or higher or similar correlations than SAT or ACT scores to college GPA. This particular study does not mention HS GPA.