Karnak, no P-38 can turn with a Spit in the game. However, they can force a gun solution and "stuff in" a shot before having to go easy on the stick to avoid real stall.
In AH1, almost all planes could do this. Just at the brink of stall, when you need a little bit more lead to hit the target, you can momentarily yank the stick back, take a shot, and ease off.
In AH2, only the P-38 can do that. Couple that with the efficient flaps, and the P-38 can gain a gun solution against almost any plane, however extremely the target is turning. Most P-38 pilots who can do that easily, also have a keen sense of gunnery in most cases. So once a P-38 grabs somebody by the tail, it will most likely shoot the target down before the turning really gets prolonged and the true difference in turn rates/angles show off.
This isn't really a "turn" at all, but sort of forcing the pitch angle up over the limit for a short time. If the situation is reversed and an at least decent Spitfire pilot first latches on to a P-38, the P-38 can't really 'outturn' it to safety.
People usually refer to that situation as "outturning", but it isn't. Force of habit I guess.