I also attest to them rampaging a lot as I was puller and cought its rampage on about half of the pulls.
Also, I think that these mobs are the ones that see thru invis more often than the others so con them if you are running to a camp location with invis on. They have a normal aggro radius and normally mitigate slow like all other mobs but snare sticks on them ok so you can play a little game of keepaway if you get into tuff times as long as you are not in a tight area.
These mobs do rampage, some do it alot and some only once so it's random. also have a 690DD proc that they will hit with alot, quads for 600-800 frequently