Pump curve, system curve data needed to determine change in pump speed:

Affinity laws state that a change in pump speed has a cubed effect on the required power. However, when pump speed is changed, the resulting operating point will likely move left or right on the curve, relative to the Best Efficiency Point (BEP). So actual required power may be significantly greater than or somewhat less than the cubed proportion.
Only with the pump curve and system curve data can change in the power required be determined for a change in pump speed.