For recon, the desired properties is speed and range, that the P-51 did do better than the P-40The P-51D didnt replace the P-40N or any other version of the P-40. The British tried the P-40 in the tactical recon role and it couldnt do it, the Mustang Mk I could and did until the end of the war. Rate of roll is a technical discussion, it has been posted here that many post war P-51s were and are rigged with a different aileron maximum deflection to that used in combat in WW2. By the time the P-51D was introduced, mid 1944, which theatre would a P-40 be useful in?