The only way to settle this thing is with facts & figures. There are some caveats that have to be mentioned right off the bat
- Lockheed P-38
- Was designed first and foremost as a day-fighter
- Disclaimer: Some will immediately say it was an interceptor, but that was just an excuse to get around undesirable requirements. The people issuing the specs wanted a plane that was usable for both offense and defense, but had heavier armament (1000 pounds of armament as a starting point instead of 500, which was the rule), and more engine power (which lead to the desire for two engines, which was verboten with one crewman). A lieutenant cannot legally override a colonel or general, so they decided to call it something other than a fighter.
- While it did other missions including reconnaissance, night-fighter, fighter-bomber, path-finder, and level-bomber (it might have also hauled a person in the nose once or twice), it was firstly a day-fighter.
- Was designed first and foremost as a day-fighter
- De Havilland Mosquito
- Was designed first and foremost as a bomber & reconnaissance aircraft: And I'm not totally sure the reconnaissance role was there for a purpose other than manufacturing a case for the aircraft's production if the Air Ministry wouldn't get attached to the idea of an unarmed bomber.
- While it did quite a number of other roles including: Night-Fighter, Fighter-Bomber, Target-Tug, and even Transport, that was not it's primary mission.
- Time period: After all, there is no realistic point in comparing a P-40 to an F-22. The variants should be compared by time-frame.
- Performance: This is basically subdivided into several areas
- Speed
- Level-Speeds: This should include the maximum overall speed, maximum cruise-speeds, and typical cruise-speeds. These should be factored, when possible, across the tactically useful altitudes. Ironically high-speed cruise is more useful a figure than the top-speed as this would be what you'd probably see when combat starts. These should be measured at weight figures typically seen at the start of combat. Don't factor in the speed of one airplane weighed down to the max with racks hanging off of everything, and drop-tanks with the other lightly loaded, and completely clean.
- Dive-Speeds: This should both factor in airspeed and mach-number. I'm pretty sure the Mosquito would come out on top in regards to mach number, though the P-38's with dive-recovery flaps should be considered as mentioned. I wouldn't weigh it as much as an airplane that could achieve that mach number without them, as it's a sign of better wing-design (plus not all P-38's were fitted).
- Acceleration: This subdivides into
- Level Acceleration: This is pretty much self-explanatory, acceleration rate varies with speed and altitude. Some aircraft will out accelerate another at all altitudes, others just at some. The condition of the aircraft should be that typically seen in combat-trim.
- Dive Acceleration: There are aircraft that don't have the highest dive-speeds, but can accelerate real fast in a dive and be on you before you can reach your peak dive speed. The Spitfire had an unbelievable maximum dive-speed (placard limit 0.85), but a P-47 might very well out-accelerate it in dives (placard limit was 0.745)
- Altitude: This subdivides into...
- Critical Altitudes: This should be factored with ram compression and equal power settings (i.e. normal rated, military, war emergency power)
- Service Ceiling: As before
- Climb-Rate: This subdivides into
- Continuous Climb: Self explanatory
- Zoom-Climb: Some aircraft don't have the best steady-state climbs but they can zoom-climb well (the P-47 comes to mind)
- Roll-Rate: This subdivides into
- Responsiveness: How quickly the rate of roll-builds from when the pilot moves the stick
- Peak-Rate: Basically, if you throw the stick to one side and hold it there long enough, you reach a peak roll-rate.
- Rate of Turn: This includes several areas of importance
- Corner velocity: The CAS at which you can pull the maximum rated g-load. Predictably varies with altitudes.
- Responsiveness: Some airplanes build up g-load / rate of turn faster than would others.
- G-load: The P-38 was stressed for a higher g-load than the Mosquito
- Speed
- Armament: This includes rate of fire, ballistic accuracy, and weight of fire. I wouldn't be surprised if the Mosquito was better in this regard as it had 4 x 20mm.
- Ease of Handling: Control forces, control harmony, stall & spin characteristics, engine-out characteristics, etc...
- Human Factors: Cockpit layout, visibility, etc...