Rebuilding a WWII Legend: The Greek Spitfire | Inside The Spitfire Factory | Machina 

Better still a steel hammer faced with aluminium or an aluminium drift.

A Mustang P51D speed was 437 MPH a Spitfire MK 14 speed was 448 MPH. These Aircraft where the later versions. Also the climb rates where Mustang 3,200 ft a minute the Spitfire 3650 ft a minute. So the the MK 14 Spitfire was faster and climbed quicker. If you said an earlier Mk of Spitfire withe same engine as the Mustang, the Mustang was about 30MPH faster. Later Mk of the Spitfire had the 37 litre Griffon Engine as opposed to the Merlin. The Spitfire was optimised as a relatively short range Air Superiority Fighter the Mustang as a Long Range Air Escort Fighter. The Mustang was originally built for the RAF by the US company North American Aviation who where approached to build the P40. North American Aviation said they could do better than that and built the P51, it was fast a low level but due to lack of adequate boost was not fast enough at fighting altitude. Five Mustangs had engine swaps to Merlin’s and it transformed the Aircraft. The US Eighth Airforce got very interested real Quick after that for long range escort role plus many other roles. It had the highest controlled dive speed of the US built fighters causing the US commander to chose the Mustang as the plane to focus on rather than the Lightning or the Thunderbolt. Lightnings where removed from the European Theatre of operation and the Thunderbolt focussed on ground Attack. The Lightning and Thunderbolt suffered from compressibility problems (Loss of Control in high speed dives) the Lightening Especially at lower speeds than the Mustang. LeMay had heard of many pilots lost last seen in a high speed dive and had them tested. The Mustang had the best Compressibility figures so he focussed on using the Mustang for the Fighter role at altitude.