[quote=@LeeRoy]
[@ImportantNobody]
The sound wouldn't be traveling faster if they spoke faster. Just their mouths. But if they were talking at supersonic speeds they would be producing sonic booms with their lips.
[/quote]

I'm thinking if they have to create sonic booms to speak then the words turn incomprehensible due to compression of the sound waves so you'd have to physically slow down to sub sonic speeds for the words to hit you and still make sense. My characters would likely have enchanted communication necklaces or whatever to speak into that communicates instantly across any distance to eliminate this problem and other uses, of course. 

Funny picturing someone sonic boom talking and sounding like gunshots/whips. You could create an intelligible language out of different sonic boom noises, but English I think not. Maybe I should have an alien race for my scifi setting communicate via sonic booms. XD some communicate through color and pheromones. That subverts the trope of scifi stuff have tons of blinking colored lights on panels because that's actually their long range communication, devices detecting color changes of them and transmitting it.

Edit: for talking is a free action, perhaps someone has the power of tropes so compels individuals to stand there listening to his monologues rather than attack. He has many powers that should be fun. However, strong will can break some of the tropes.