Without a speed limit, I'd take i-70 from KC to STL at about (160~mph) 250km/h for 95% of it. I'd make day trips just to get white castle at white knuckle speeds.
I don't think that is your average American! At least I hope not ;)
I-70 is a mostly straight highway with a divider, it'd be pretty safe as long as it's not crowded. Autobahn speed limits are certainly doable in many of America's highways.