So, I've made a couple of replicas now where the maximum speed was know. But at what altitude? The XF11 is supposed to top out at 450mph but is that at 500ft? Or 30000ft? Same deal with the N1 max atmospheric flight speed of 1100kph just shy of the sound barrier (which I think is too slow personally) but is that at 14.7psi (sea level) or at any atmosphere. Or maybe it's governed when below 80k ft. Any thoughts?
@RodWan search for more detailed data for the aircraft. It will give you Vmax (maximum velocity) at H0 (Sea level) and Hopt (optimum altitude, maximum speed achievable in level flight). For example, you have mentioned XF-11. Here's an entire operating manual for XF-11
@RodWan The thing most builders neglect is stall speed, imo.
Well, that's my point, it's not always possible to know how it high it was intended to be. I think the major issue is that the game is telling you mph ground speed and max speed for airplanes is measured in air speed as it has more to do with structural integrity and pressure then anything. But either way it's kinda a guess like you said @F104Deathtrap
For most WW2 aircraft equipped with turbochargers, their top speed was around 20,000 feet. For those without turbos expect it's maximum performance at lower altitudes like 10,000 feet. Jets often achieve top speed at very high altitudes, above 30,000 feet but it depends on the engine, some are designed for lower altitudes.
One way to guess is to learn how the plane was used and flown.