How is diving countering a Spitfire? Also, please explain how diving away from a Spitfire Mk VIII, IX, XIV, or XVI is going to save you? You have to be careful with the P-38's speed in a dive, these Spitfires will be able to keep up with you and will get you as you level out in a dive. Sure, with the built up energy you might be able to keep them out of gun range for a few minutes but eventually they'll catch up and you'll have to fight.
ack-ack
Spitfire is not the best at high speed (not talking about XIV), therefor in planes such as P-51, Tiffy, temp, 190D, 109K, or F4U-4 you should be able to get away if not starting at low speed. Then thous other slower airplanes are capable of out turning a spitfire and winning that way. Spitfire can do everything, but it's not the best at anything. So as long as the other pilot does what did aircraft is best at, he should win. Plus it's not the airplane, it's the pilot that matters.
I would call it the best, but I would not say that it should be perked (well...maybe XVI).