A few things for those who do not know to consider.
The P-38 had a rather thick wing, called a high aspect ratio wing. It was there for two reasons. One, there is no place in the P-38 fuselage to carry fuel, and the P-38 was designed to be a long range high altitude bomber interceptor. That means it was intended to fly over 500 miles one way, at high altitude, and intercept enemy bombers. So it needed a lot of internal fuel capacity (there were no drop tanks being used in 1937/1938). And in the original design, the intercooler was in the leading edge of the outer wing, so there was no fuel in the outer wing. Only in the later J and L models did the leading edge of the outer wing become a fuel tank as opposed to an intercooler. The other reason for that thick wing, once it was chosen to allow for fuel capacity, is for its climbing ability. That high aspect ratio wing meant that although the P-38 carried a fair amount of weight per square foot of wing, the actual wing loading was easily handled by the more efficient (for climbing) high aspect ratio wing.
When you compare wing loading simply by pounds per square foot, and ignore the wing profile itself, you give yourself a false result, and you are not accurately comparing true wing loading.
The fault of this thick wing was that at higher speeds, it forced air to accelerate to speeds between just sub sonic, to super sonic. The wing itself, by design, was speed limited.
Early on, they changed the radius of the fillet joint where the wing joined the center nacelle. This joint was actually so critical that the fit had to be perfect from the leading edge all the way past the cockpit window. Any problems with the fit there lead to instability and early onset of compression.
While the P-38 was heavier than a P-51, it also had over 3200HP (in the P-38J, the P-38L had over 3450HP), and that 3200HP was producing thrust through two propellers. So, the P-38 had nearly double the HP of the P-51, but it was not double the weight, and the HP of the P-38 was generating its thrust through two propellers. So, once again, when you compare power to weight, if you ignore the difference in thrust, you also get a false result, preventing a correct and useful comparison.
Fowler flaps not only change the shape of the wing, and do so while creating less drag, they also change the chord and the aspect ratio, which makes them a good bit more efficient than other flap designs. And the Fowler flaps on the P-38 were, according to most, more efficient than the Fowler flaps on the P-47.
The dive flaps installed on the P-38, according to Kelly Johnson, added very little drag. The reason for this is they changed the shape of the wing, and reduced the high speed turbulence that was a part of the compression problem. The turbulence created as part of the compression problem caused a serious disruption in air flow over the wing, actually increasing drag. That is why if the dive flaps were deployed after a dive began, and after the onset of buffeting, they would momentarily increase the buffeting, before reducing the buffeting. But they would not slow the plane down. Some pilots reported that the plane actually increased its speed after the dive flaps were deployed. The dive flaps also gave a momentary "pitch up" of about 15 degrees if deployed when not diving.
