In the yard debris recycling yard I worked in we used a WHO tub grinder with a turbocharged supercharged Detroit in it. That tub grinder would pulverize a 3ft in diameter tree stump in a matter of seconds into chips no bigger than a few inches, it was impressive.
I doubt people realize just how big the jaws are on the crane and just how fast it goes from pile to shredded. When you compare it to the person standing beside the machine it will blow your mind.
When adding a new quarter mile entrance ramp to the highway they used one of these monsters along with three excavators to keep feeding it, big, whole trees it devoured...ive never seen a bigger piles of chip..