RE: Spitfires?
They are good heads if you have the energy to use them. Because they are held closed by friction they seem to require a bit more energy than some of the other heads.
Me and a buddy used them several years ago and didn't have much luck getting pass throughs. However I was shooting 26 inches and 60 lbs. And he was shooting 73 lbs at 27 inches, but it was an older darton bow with round wheels, so he was probably shooting about the same speed and KE I was.
Paul