Curlycherry1
Addicted to ArboristSite
The only one I know capable of doing it that fast has to be trucked in on a lowboy. It is essentially a skidder, with a huge stumper attachment but I am certain it would be more than the ho could afford.
Are you thinking of a Hydra Axe 721? The tree clearing outfits around here (and there is a good size handful of them) use those beasts. In Stillwater, MN a few years ago one outfit cleared a swath of land with 4-6' diameter oaks, old growth monsters. I watched a Hydra Axe eat a ~5' stump in about 10-15 minutes. Garbage flying in every direction when that thing started eating that stump. They left many of the stumps 2-3' above the ground but it did not matter to that thing. Hydra Axes are really popular around here and due to the economy there are a lot of used ones available now.
Here is what they look like with the brush attachment. If it can push the tree over the brush grinder can eat it. I have watched them walk through 4-6" trees like they were mowing a lawn.
Here is the 34" stump grinder for that beast. Now that is a machine <insert Tim Allen grunts here>