The p51B is a real sleeper all right - it was my favourite ride in AH1 too. I'm just a mediocre stick in a dogfight, but the p51B appears to have an energy edge over the 'D' in a one-on-one. I think that the 4x.50 guns and the laticework in the canopy discourage a lot of people from picking this sweet ride more often. The truth is that the 4x.50s are all you need against nme fighters, if you can hit with them - although I admit they aren't so good versus buffs. Plus people seem to take the 'B' lightly when they face one, figuring that it's "not dangerous". This, of course, is a mistake.
I like the olive drab paint scheme best as it is better camoflage then the silver schemes used for the 'D', and I know I find it harder to see and hit AH planes that have good camo, icons or not, in low level fights. I may fly the 'D' more often in AHII than before now that an olive skin is available for it.
I'd love to see the 'C' model, or anyway Malcolm hood upgrades to the 'B' available in AH2 someday. Being a canuck I'm required to have a special fondness for Spitfires - and I do, but the AH plane I feel most at home in is the Mustang III (P51-B).