Only things with p51 that bothers me, is its fuel capacity and kind of strong weapons (v0.36, pea shots, v0.37, zipped death star)
About fuel capacity, it flies for over hour with full tanks and so on, where 109/spit/la5 flies barely few minutes.
As a bonus it has now strong guns and lots lots ammo. (hmm, perhaps .50s are realistic after all, but cannons don't work anymore on anything)