For an Me 109GG the following speed improvments were possible compared to an standard aircraft operating a 1.3 ata boost at 0 meters altitude at around 483km/h
Streamlined cowling to smooth over MG131 bulges
483km/h-> 489km/h +6 km/h 1.24% (Test Carried out on a G6 with MG131 gun bulges)
Fully Retractable Tail wheel..........................................…...…...
494km/h-> 506km/h +12km/h 2.37% (Test Carried out on a G1 without bulges)
Fully covered wheels
..........................................………..506km/h-> 516km/h +10km/h 1.97% (Test Carried out on a G1 without bulges)
Percentage......................................................................................................…...........Total 5.58%
The effect on a 397mph Me 109G6 at 1.42 ata is 397 mph x 1.0558 =
419.15 mph.
Kurfürst - Influence of the shape the engine cowling on the level speed of the Me 109 G and
Kurfürst - Leistungzusammenstellung Me 109 G. (no English version so)
It should be noted that the P-51D had all these features : retractable tail wheel, fully covered wheels and of course no gun bulges. With fairly minor modifications that Me 109G6 could have been 22mph 35km/faster but production priorates were put ahead of quality and Luftwaffe pilots had to suffer.
The lack of a high altitude supercharger explains the rest of the speed gap. When the Me 109K4 came into service it had all of these features plus and enlarged supercharger and the speed was the same at around 20,000ft-25000ft. The P-51 was superior at sea level.
The P-51 Laminar flow wing was superior to the Me 109's but this manifested itself only in the thick air of low altitude where the lower parasitic drag of the P-51 was unbeatable. The laminar flow wing was only slightly more laminar and this was not a big advantage but it had 2 big advantages: 1 It had a much higher mach limit which meant that the rise of compressibility or shock wave drag was less at the speed the Mustang operated which was Mach 0.55 (at sea level) to Mach 0.66 (at 30,000ft), it was this rather than laminar flow that made the mustang more efficient. it also helped stop the ailerons from locking up from compressibility and helped the P-51 have a high roll rate. 2 The other factor was that the wing was much thicker which allowed space for the fuel which gave the range the P-51 was famous for. This also allowed a stiffer wing.
The Germans understood laminar flow technology and 3 aircraft were planed with laminar flow wings: the Me 309 (all their own work), the Blohm and Voss BV.155 and a planed improved version of the Dornier Do 335. The work on the Me 309 was all their own. The Japanese also introduced several laminar flow wing aircraft.
The Hawker Tempest had laminar flow wings, the thickest point was a little further forward than the P-51 and the wing cross section of the Tempest seems the same as the Me 262 to me.
The follow on of the Me 109K4 was the Me 109K6 which incorporated two MK108 30mm integrated wholly inside the wings. I suspect this would allow an elimination of the cowling guns or at least a return to rifle calibre machine guns. The Me 109K14 had a two stage supercharger (without intercooling but with water injection) and was expected to reach 457mph.
So apart from range the Me 109 remained theoretically competitive. It was clear it was on its way out. Yes the Mustang (and Tempest) was superior but remember the same cant be said of other allied fighters such as P-47, P-38 (superior high altitude performance due to turbo-superchargers) nor the Typhoon or Spitfire or Hurricane or P-40 or P-39.