(Image removed from quote.)
This is worth taking about. First is it a 2D section lift and drag plot from wind tunnel result at a specific Reynolds number - with no induced Drag so the entire Drag component is Parasite Drag. The introduction of a finite wing reduces the Max L/D as Induced Drag is introduced. For a very large AR the comparison is close.
You can note that the range of 66-415 superior CL/CD ratio (over 2315) is much broader than the 0.25 to 0.5 CL range. All things equal this a/c will exhibit far better Drag reduction across most of the performance envelope until in the lower speed range where CL has to increase due to angle of attack increase to maintain level flight.
Vraciu's comment that laminar flow was not achieved is true in a practical sense, although the Mustang surface prep on flush rivet construction, filling, sanding, priming and painting did delay boundary layer separation. That said slower velocity gradient of the 'laminar' flow airfoil delayed pressure gradient induced separation ---- and a fundamental reason why a 'fat wing' NACA/NAA 45-100 Low Drag wing had delayed shock wave formation over conventional airfoils (like the 2315).
That said the actual real life low drag result was achieved - just not to expected theoretical laminar flow objectives. As a contrast - The CDparasite of the P-51 at RN=9x10^^6 =~ .017 while the F4U and F6F comparable parasite Drag values, all derived from full scale wind tunnel testing, is ~ 0.26 and 0.27 respectively. That is mostly wing and both the F4U and F6F had, IIRC 23015 section airfoils (Ditto P-38 and FW 190 and F8F). The Total Drag comparisons between the latter five fighters varied primarily due to Induced Drag via AR.
To toodle back to our discussion, looking at the respective Total Drag vs Velocity plots for each fighter yields a plot of CDparasite which increases from CDzero lift (low) and a CDinduced which starts high and decreases non-linearly from low speed to high. When you look at each plot, where the two curves cross is CDminimum.
THAT is the Golden strike zone for fine tuning speed vs engine settings to get maximum mileage per pound of fuel - for That altitude, That GW, That External Drag condition and it changes every minute as fuel is consumed, lowering GW and reducing AoA required for level flight.. and so on.
Why does the F4U, et al - Never- get the same range attainable, per pound of fuel carried, nor cruise at the same relative high speed for that Golden Strike zone, you ask? They all start with 50% more parasite drag - which shifts the plot to the left (Lower airspeed at the CD=CL bottom of the plot) - AND only the Allison had essentially the same (or better) fuel consumption for same MP/RPM- all the rest had gas guzzling powerful radials.
