At what speed does the benefit of a zoom climb become negligible?

The benefit of a zoom climb becomes negligible at 150 KIAS due to the dynamics of aircraft performance at higher speeds. In a zoom climb, the aircraft utilizes its kinetic energy (speed) to gain altitude, effectively trading off forward motion for vertical lift. As the speed increases, the maneuverability and efficiency of this climb decrease.

At 150 KIAS, the aircraft is approaching a speed where aerodynamic drag begins to significantly impact climb performance. Beyond this speed, the added kinetic energy is not as effectively converted into altitude gain, making the advantage of the zoom climb less pronounced. Essentially, while the aircraft may still gain some altitude, the efficiency and effectiveness of the zoom climb are compromised due to increased drag and reduced thrust-to-weight ratios at higher speeds.

The other speeds listed do not exhibit this effect as prominently; at lower speeds, the trade-off between altitude gain and airspeed still yields clear benefits in performance, allowing for an effective zoom climb.