My typical driving habits are to plug the cruise control right around the speed limit. Sometimes I'll find myself drifting the speed a bit past that, but I don't blatantly speed most of the time.
Door-to-door for me is about 220 miles (I376 E --> US22 E --> US 220 N --> I80 E)
If one could go at highway speeds the entire time, that's a bit over 3 hours. Factor in that some of the trip isn't major highway, and at least one bio break, and there's the 4 hour transit time.
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--Greg
http://www.pobox.com/~gregleg/