WOW,,,, .43 for the GT-40 is a "drag"! I would guessed it would be in the low .30's based on "looks". Thats the thing about CD, it's just really hard to measure without the right equipement. And "looks" can truly be deceiving!
Of course many race cars use various "aero" functions to put down force on the car. This causes the CD number to go up by increasing "drag" but the car STAYS on the track! You got to find the right balance between speed and staying on the ground! "Loose" is fast, but the "risk" goes up!
Running the "flats"? We don't need no stinkin' wings or spoilers to slow us down!
Ernie