I was curious if a tracked vehicle could ever be fast enough to compete in an extreme off road rally like the Dakar, so I googled “fastest tracked vehicle” and came up with the Ripsaw vehicle created by Howe & Howe productions.
At 80mph it beats the M1, but is probably still to slow to win a rally. Still very impressive creation with 450hp blown 427 and 14 in of suspension travel. Autoblog has a nice description and video, and the makers have a less useful site with some pictures and broken video link.
Update: New post here