Well, there are two Airacobra versions available, and both do differ a bit in thier capabillities.
The P39D is a bit underpowered and heavier as the P39Q, but it has the overall way better weapon package when taking the 20 mm option.
This bird is quite a nice turner, but lacks vertical performance and acclereation. A smooth flying style is really rewarded by this plane, and the gun package has a long reach, so you can keep the fight more "loose" and the deficites are not so appearant than they would be in a close fight.
The P39Q in the clean configuration (sans gun pods) has a much better power/weight ratio and therefore superior in turning, accleration and vertical performance. However, the gun package is difficult to master, since the 37 gets very difficult to aim at longer distances, and 2 .50s with just 400 rounds arent that effective at range too. However, in a close fight, the 37 mm is deadly, one ping and the con goes "boom". But with the increased flight perfomance, you can afford a closer fight in the Q, so that is not that much of a problem anyway. As for the wing pods, I do not recommend them. They add condiserable drag and weight, and they arent terribly effective either.
Personaly, I choose the D for furball type of engagements because of the gun package and the clean Q for more controlled enviroments, where raw power will make the difference.
