I have been DH racing since 1985. I did well at the masters world championships. The race is crazy because of the fence and dog etc. the actual terrain is pretty modest.

Watch this film of world champion Sam Hill. It would take 2.5 hours to drive down this hill in a 4X4 truck. I think it took Sam around 3 mins.
http://www.youtube.com/watch?v=mIygwolIHjg