Very efficient laminar flow wing?
I'm afraid not. Very little laminar flow existed. From NACA
Though the Mustang's war record confirmed expectations of appreciable improvements in speed and range as a result of the low-drag design, practical experience with this and other aircraft using advanced NACA sections in the 1940s also showed that the airfoil did not perform quite as spectacularly in flight as in the laboratory. Manufacturing tolerances were off far enough, and maintenance of wing surfaces in the field careless enough, that some significant points of aerodynamic similarity between the operational airfoil and the accurate, highly polished, and smooth model that had been tested in the controlled environment of the wind tunnel were lost.* Still, despite manufacturing irregularities and the detrimental effects of actual use, the Mustang's modified 4-series section, with its pressure distributions and other features, proved an excellent high speed airfoil. The delineation of it and other laminar-flow airfoils was thus a great contribution by Langley, even if not exactly to the degree advertised by NACA publicists like George Gray, who claimed in Frontiers of Flight that "the shape of this new wing permitted the flow to remain laminar until the air had traveled about half way along the chord." According to Langley engineers who knew what it took in practice to achieve success, Gray's claim was an exaggeration. Because the percentage drag effect of even minor wing surface roughness or dirt increased as airfoils became more efficient, laminar flow could be maintained in actual flight operation only in a very small region near the leading edge of the wing.
* After the Two-Dimensional Low-Turbulence Pressure Tunnel was put into operation in the spring of 1941, Langley researchers undertook a systematic study of the 63-, 64-, 65-, and 66-series sections. Working 48 hours a week each in three daily shifts, the men of Jacobs's section ran these tests at Reynolds numbers of 3, 6, and 9 million, with smooth surfaces and with a standard carborundum roughness on the leading edge. Though results made it clear that ideal laminar-flow airfoils were practically impossible to achieve, Jacobs would not let this information be published. Only after Jacobs resigned from Langley in 1944 did the NACA finally publish a report stating this conclusion: Laurence K. Loftin, Jr., "Effects of Specific Types of Surface Roughness on Boundary-Layer Transition," Adv. Conf. Rpt. L5J29a, 1946.