We have the best possible 109K in the game, and it is significantly faster than the P-51D on almost the same power. With 100/150 grade fuel the Pony should edge out the 109 though. Pitty we don't have that as perk-fuel or something. Souped up Spits and Ponies would be awesome, even if we could only fly them once in a while.
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For unknown reasons I can't explain I revisited this thread
Your data on the P-51D doesn't reflect the later Flight Tests for your speed vs altitude and Hp ratings. Two significant points on the May 1945 test results below. First, the top speed of 442mph at 67"/3000RPM at 26,000ft with 1410Hp - is With external racks. The improved racks for D/H achieved about 50% reduction in drag penalty overP-51A/B racks. For purposes of this comparison you should find Flight testing of the K with Schlob 503 rack inclusion for your 109K speeds.
I exchanged a lot of emails with Dr. Millei (Kurfurst) to try to get best individual comparisons between P-51B and various ther fighters, normalized to full (internal) gross weights, including 109G-6 (including DB606A/S. I included those in my book (co-authored with Lowell Ford) P-51B:North America's Bastard Stepchild that Saved 8th AF" (agree to a little hyperbole).
Didn't find a 'racked' 109K at full combat load that exceeded 440mph. Your source? From your source, what were the conditions at takeoff and FTH?
Further comment - you rebutted 'much larger' comment of Mustang compared to 109 (all) as in 90% range but that isn't representative of 'size' relative to area, volume or drag.
While the Linear span of a 109 is about 90% of the 51, the AREA of 172x2= 344sf to P-51 235x2= 470sf, a 70% factor with similar effects for all wetted area. It is much smaller - and yet according to Hoerner, chaper 14-9 the CDw=.0095 for the109, to P-51 CDw=0.0040.
You might also note that MILITARY Power at 29K results in 439mph in the P-51D-15-NA with the 1650-7 developing 1288hp.
http://www.wwiiaircraftperformance.org/mustang/p51d-15342.htmlBTW - this Reports also is a strong reference to the final range tables of the P-51D.