There's 2 main kinds of drag operating here. A total drag graph is U shaped.
At lower speed **for the plane with wing loading a big factor** is induced drag. This is a real killer for the FW's until maybe 340-360 kph.
From middle speed on up, parasite drag goes up by squares, twice the speed is 4x the parasite drag even as induced drag falls due to lift squaring with increased speed allowing the nose to drop while keeping level flight. (trim)
Ps is excess thrust, total thrust minus drag. The faster a prop plane goes, the less thrust it has which is where the steepness of Ps curve at high speed sets in. It's not a constant minus the drag U but a downward slanted line minus the drag U.
I just had a look at La5F vs La5FN (IL2C 4.07m) and the La5F Ps curve looks the same as the La5 Ps curve when switching back and forth.
What's the difference between a Spit VB and a Spit LFVB besides supercharger?
At 240 kph, Spit VB = 13.5 -- Spit LFVB = 17.3 --- 128%
At 320 kph, Spit VB = 10.5 -- Spit LFVB = 15.5 --- 148%
At 400 kph, Spit VB = 3.8 -- Spit LFVB = 9.9 ------ 260%
At 430 kph, Spit VB = 0 -- Spit LFVB = 7 ----------- PWNED!
What % longer will the Spit VB take to reach 440 kph in level flight? If 50% longer is insane then what is forever?