Okay, we all know the car has less drag with windows closed.
I also read somewhere that 45 miles per hour is the crossover point for AC vs. windows.
If you are going OVER 45 close the windows and turn on the AC for best MPG.
UNDER 45, open the windows and turn off the AC.

Now, when the windows are open I would guess that opening only the front ones would be the worst for MPG because the air coming in the front cannot get out the back.
I'd guess opening all 4 windows half way would give better mileage than opening only the front two all the way.

What about opening both windows only on one side?
Any mechanical engineers here?

Need fewer troops to support.
Drive a hybrid.
Best tank 71.65 MPG.

Before this car I spent two years learning hypermiling on my 2004 HCH1.