https://www.researchgate.net/publication/256606781_The_Effect_of_Interior_Aircraft_Noise_on_Pilot_Performance?utm_source=chatgpt.com
This is a study that sayes what I say. Here is short conclusion:
Open cockpit flights expose the pilot to extreme aerodynamic flow and noise, with negative impacts on performance already noticeable at speeds above 250 km/h (approx. 135 knots) and with increasing speed above 400–500 km/h (typical for WWII fighter aircraft), these problems become critical.
Key influences and their manifestations by speed:
Noise (above 100 dB at >300 km/h):
Engine and aerodynamic noise increase with increasing speed.
Noise above 100 dB (commonly measured in open cockpits of WWII fighter aircraft) causes reduced attention, impaired decision-making and long-term hearing damage.
Wind (significantly above 250 km/h):
At 250–300 km/h, wind begins to make it impossible to turn the head comfortably, visual accuracy and reduces reaction capabilities.
Above 400 km/h, the wind is so strong that goggles or a helmet must be extremely strong, otherwise there is a risk of tearing them off.
Combined effect:
The combination of wind and noise at speeds above 400 km/h significantly reduces situational awareness, tires the pilot and impairs the ability to react to crisis situations.
Consequence:
Studies confirm that problems with hearing, vision, communication and concentration begin at speeds above 250–300 km/h without a cockpit. These effects worsen significantly with each increase in speed, which led to a design shift towards closed and pressurized cockpits.