Lansing, IA to La Crosse, WI

You'd be better off going up the MN side if you want to get more gravel than pavement.  I've ridden my moto on both sides and coming down from Mpls we were on probably 80% dirt and going up through that section of WI was probably 80% paved.  I don't have a route for you but it'd be easy to scout one on google maps.

Good luck!