The 38s have a sweet spot you have to learn to fly in.
If your trying to stay fast, 350+, then you fly it like a p47, or p51. Smooth climbing turns conserving "E", making the enemy burn"E" with each run you do on him.
Slow speeds, under 200 you run the flaps in and out as much as posible. Roll them out as you slow and turn, or roll over on a loop, bringing them back in as fast as you can to get your speed back up, and rebuild your "E".
In the middle ground, 200-350, you use it both ways. Keep your turns and such smooth, but go ahead and drop a notch of two of flaps to get that bit more on the turns, or loops. At the middle speeds, side slipping and chopping throttle works great, and the acceleration can get you back up to speed pretty quick.
Its all a matter of "feel", and like all other fighters, knowing the enemies "E" state is what can save the day.