I'm doubtful you can outride the speed capabilities of the MTB. I've hit 32 mph on slight downhills, pedaling my legs off, and 28+ coasting downhill. (I always roll fat knobbies.)

My co-worker/riding buddy used to commute on his Epic; he hit 39.9 one day going home.

What's the world record on a DH bike? 80mph or something?