I've had a bit of luck finding youtubers/twitch streamers who are content to let some dead air go by if they don't have anything important to say, and definitely don't do any yelling or screaming. It's a real nice change.
Partially I'm just making this post to share the few I've been watching the most:
Jagged Appliance, a Supreme Commander player and caster.
Growling Sidewinder, a DCS pilot who goes into detail about dogfighting and BVR fighter jet tactics.
Tasteless, a Starcraft caster who plays Brood War and chess in the Korean timezone.
I'll add lethalfrag to the list. He's easily my favorite twitch streamer, always very calm, plus during breaks you can watch his cats play.