What a coincidence it would be if people's optimal speaking speed, both reading out loud and conversational, was equal to their optimal audio comprehension speed. There could be some evolutionary justification for this to be true, but it would still be remarkable.

I would love to find data on listening comprehension based on audio speed and activity, whether it be lying down, driving, doing chores, walking, or exercising. My intuition is that there are many people that best comprehend the material at around 1.5x-2.0x and comprehension drops precipitously at both ends. My guess is that, as with many mainstream broadcast choices, the canonical broadcaster voice is purposefully slow to cater the widest possible audience, including ESL listeners.