I have also noticed, many people speak too quickly in their presentations. Speaking quickly can bring energy and momentum to your speech, but if you don't vary your speed, your audience will stop listening. They are just too tired to keep up with you. Let your words resonate in the air. Let important thoughts linger, let emotional moments land.
Variety is best.
In my seminars and coaching, I encourage my clients to explore how it feels to say words very slooowly. . . . We practice saying words loudly, as well as very softly. By practicing in this way, we teach our unconscious mind that there is more than one way to say something. Sometimes when people begin working on their voice they no longer sound monotone, but they may sound a bit artificial. Our voice must sound authentic.