Setback does several things to a boat. Primary functions are increase in leverage and increase in motor height. Increased leverage allows you to lift your bow easier, less whetted surface = greater speed. Unfortunately at low speeds it tends to cause a boat to porpoise ( a fact of life with large setback rigs ) . Increased motor height allows you to lift your motor higher. This helps you turn higher rpms. Higher rpms = faster as long as your prop doesn’t start to slip. Drawback there is loss of holeshot. The perfect setup for your boat depends on a lot of things. The Hp of your motor, the loaded weight of your boat (200 lbs of gear changes my set up significantly), your pitch and make of prop, the max rpm you can turn that prop. Arm yourself with that information, and go to bassboatcentral.com. Click the setup expert link. They have a setup expert for tritons that can help you pick a setback, prop and motor height, for your specific rig.
The setup on My 21’ Stroker : 13.5” setback on a detwieler hydraulic jackplate. 280hp Merc racing motor. 27” trophy 4 blade. @ 7800 rpm i’m running ~95mph depending on boat weight. 2 peeps in boat tournament load im 92-93 mph. My best recorded gps speed was late last year 38 degree, dry air ,no gear in boat ¼ tank fuel 29 pitch 3 blade tempest. 105.4 mph