As Promised!
First some wind resistance data on trains, automobiles and ships
Now, the effect of yaw wind on trains and wind resistance on various bodies
What you should take away from this is that the streamlined train has roughly half the Cd of the non-streamlined train. Also, when there is a yaw wind involved, the longitudinal force on the non-streamlined train nearly doubles, where the streamlined train is almost unaffected.
In response to the 200x question, I used the Aerodynamic and rolling resistance calculator. I simply changed the mass and the Crr.
Run 1. Crr=.0002 Mass=200000kg
60mph - 37.5 hp
Run 2. Crr=.008 Mass=1000kg
60mph - 26.25 hp
So yes, that is really close, especially if the semi doesn't have that good of a Crr!
Run 3. Crr-0.015 Mass = 1000kg
60mph - 28.75 hp
Ship Data that may be interesting...
Ship speed = 10 knots; air resistance = 2.5% overall resistance
Ship speed = 10 knots; 20 knot headwind, air resistance = 22.5% overall resistance
similarly, small side winds may cause appreciable increases in resistance of bodies such as ships and railroad trains.
Source: Mark's Standard Handbook for Mechanical Engineers, 7th Edition, 1967.