Gears operating at high rotational speeds are prone to resonance-induced load amplification, which can significantly shorten their service life. This study quantifies the dynamic factor ( \(\:{K}_{v}\) ) of a spur gear pair operating between 500 and 4,000 rpm by combining high-fidelity dynamics simulations with targeted experiments. The simulation model, validated against experimentally measured dynamic meshing forces, accurately reproduces the primary resonance at 3,450 rpm with a mere 2.48% error in \(\:{K}_{v}\) . A comparison with calculations based on ISO 6336 Method B reveals that this standard tends to overestimate both the resonance speed and \(\:{K}_{v}\) , leading to unnecessarily conservative designs. Parametric studies show that increasing the torque from 100 N·m to 500 N·m reduces \(\:{K}_{v}\) by up to 14%, while crowning that reduces the peak-to-peak transmission error from 4.5 μm to 2.0 μm attenuates \(\:{K}_{v}\) by 22% and suppresses contact stress amplification. These findings demonstrate that validated simulations enable more accurate resonance prediction and promote more weight-efficient gear design for high-speed applications than empirical ISO formulas.