Jim: One does not travel Amtrak for speed. If your departure and destination cities also have Amtrak stations then Amtrak is good for two things: (1) Amtrak is more resistant to bad weather, like thunder storms, than the plane. (2) Perhaps because of Amtrak's better pay (at least for some crew members) Amtrak crews are generally more civilized and less inclined to make a police case out of every single slight--real and imagined.
A correction: My 7-hour figure is closer to 6.5---as if that makes any difference in terms of time. The schedules are at:
http://www.amtrak.com/servlet/Conten.../1237405732505
Under "MICHIGAN SERVICES," click on the "effective date."