My daughter took both since the school offered ACT to all students at no cost. Her SAT score was relatively higher o she concentrated on that and took a second SAT. She only submitted the SAT to schools. They weren’t that far off, and both were excellent, but we didn’t see any point in trying to bring the ACT up since the SAT was already good. If she really scores > 1500 on the SAT I would not bother with the ACT at all.