One thing you can see is the effects of propeller efficiency. Even though the F6F engine is rated at 2000 BHP, only ~1650 is available due to propeller efficiency losses. This is why power-loading is a dangerous metric to use to compare aircraft with, especially when deciding one aircraft should climb better than another with lower power-loading. Notice that Pe = 0 at max speed.
If you wanted to properly compare the climb potential of two aircraft, you can use a chart like this and plot the Pe Curves for both aircraft and then have a reasonably accurate expectation of the relative performance. Pe curves can show, for example, how an aircraft with lower power-loading can have higher excess power, or an aircraft with higher power-loading can have lower excess power.
These curves represent knowledge of total drag acting on the aircraft (both zero-lift drag, and induced drag (so you need Cd0 and Cdi), propeller efficiency, rated engine power at a specific altitude, etc. At speeds approaching transonic, you'd need to account for compressibility drag as well, and if the aircraft are maneuvering, effects of those maneuvers on zero-lift drag.
Information you'll need to have access to in order to create this type of chart: stall speed at a specific configuration (testable in-game using Badboy's Bootstrap Calculator) and maximum speed at that configuration (testable in-game), the zero-lift drag coefficient of the aircraft, rated engine power at the test altitude (either from a chart or derived by accounting for changing dynamic pressure with altitude), wing area, aspect ratio, some sort of accurate estimation of Oswald's Efficiency Factor for that aircraft. Then, using standard aerodynamic equations, plug everything into an Excel spreadsheet and start working. My spreadsheet for this chart had approximately 20 columns in it, and the curves were created using speeds broken down into 5 mph increments between 96 mph and 320 mph.
