According to the P-38 Pilots Manual. The L model with the V-1710-111 and the V-1710-113 engines, should perform as follows at max continous throttle settings (note this is not WEP, adjust engines accordingly)
RPM: 2600
Mixture: Auto Rich
Manifold: 44"
Gallons Fuel Consume per Hour: 245
So if you consider the arena setting of x2.5, the Aces High P-38 will consume 612.5 gph.
That means that a single 150 gallon drop tank should last 14 minutes and 42 seconds if you have your engines settings correct.
Easy enought test. But I am gonna go eat dinner, and let one of you P-38 drivers do the test

------------------
Vermillion
**MOL**, Men of Leisure
Carpe Jugulum
"Real Men fly Radials, Nancy Boys fly Spitfires"