I don’t ride, but some folks I know do and go fast out on the straight, deserted roads of Eastern Washington State. I have heard them be concerned about the odd piece of gravel on the pavement at those high speeds.
When you mention bumps at high speed consider my favorite sport,i and friends consistantly hit speeds of 60,70,80 mph on these types of trails.:)
http://www.youtube.com/watch?v=lpY20SOAF-U&feature=related