So you want to buy a new Mac Pro, but you’re concerned about a tiny computer producing a lot of heat? Jason Snell:
They ran 4K video on two 4K displays and I held my hand over the top of the Mac Pro. Hot air was blowing out, but I couldn’t hear the fan.
Reminds me of this, one of my all-time favourite Daring Fireball articles. For some reason, the video embeds don’t work any more (at least, they don’t on my end); here’s the first video, and the second.