First of all, for the P-38, go to CRIS, go to the Air Warrior Help and Training library, and download the help files from the CRIS classes held recently. The P-38 class on CRIS (held by Pyro, if I remember correctly) is my source for most of this info, and it works wonderfully. Those transcripts are a bloody gold mine of info. (Weren't they uploaded to somewhere on cactus, too?)
Take the P-38 seriously as a threat, I see a lot of people that don't. I mean, yeah, it's got a hit bubble the size of Delaware, but gimme a break, people, IT STILL HAS GUNS! :)
P-38 turns best around 175 knots with one notch of flaps, in a slight descent. In this attitude, it can even out-turn a Spit. Once it slows down below 150, it doesn't turn nearly as well and can be beaten by many planes, including Spit, Yak, and Ki-84.
Flaps are the key to the whole thing--in a turning fight, hit 1/4 flaps between 200-225 knots, and 1/2 flaps below 175. Retract them as soon as you can, as they really slow the bird down.
The Lightning carries an obscene amount of gas--you don't need much, even with two engines. I use 35% for long-duration flights and 25% for short-duration flights.
The 38 also has a low stall speed--you can "hang it on the props" in a zoom climb and nail people above you. Just make sure no other enemies are around, because you are very vulnerable doing this, and a heeeeyuge target.
Here's another neat trick I use sometimes around furballs--get about 5,000+ feet over the fight, doing a decent speed, and dive in. When you hit 300 KIAS, cut the throttle and use the dive brakes to maintain 300 KIAS, "pumping" it as necessary. At that speed, the roll rate isn't that bad, and the near-vertical entry makes it easy to pick out a victim. The key is to determine early whether you will vertically overshoot or not--if you're clearly not going to get a shot, start pulling out, WEP it (but be careful not to exceed compression speed), and zoom away. If you're not going to overshoot, keep laying down on the brakes and maneuver as necessary for positioning.
You'd be surprised how well this works with some practice, particularly if the guy doesn't see you till late in the maneuver. The AW mis-modeling of the P-38J's dive flaps as brakes is the key to the whole thing--without them, you'd compress even with power chopped to idle. With them, you can keep control, then slide in behind someone and cut speed to prevent an overshoot in virtually any plane. This is particularly fun to do against Spitfires, and it works.
One of these days, I'll remember to film myself doing this and upload it.
Moose