Interesting...
Without MW 50, the D-9 in the charts is quite close to the AH P-51D in performance.
D-9 is about 10mph slower at all altitudes except between 15,000ft and 20,000ft, where they are about even.
P-51D climbs a bit(~100fpm) better below 12,000ft, but then the D-9 is slightly better from there up to 20,000ft, where they become equal.
With MW 50, the D-9 is everywhere superior.
