The Pump is a 1HP Emerson with a SF of 1.65. It replaced at Pacfab challenger motor which was a 1HP Centurion 1.65SF motor. If I wanted to just swap out the motor:

Do I need to maintain the 1.65SF x 1 HP for a max HP of 1.65?

Would a 1HP x 1.25SF be sufficient?

I have a 3-5-3 pool, which is about 13K Gallons.