Yep, the K stands for "Konstant" not Kilo.

Unfortunately, you can't make generalizations like, "more power less speed... less speed more power" about two motors with different Kv ratings, like the Park 400 3700Kv and 4200Kv. Both motors are capable of handling the same amount of power; they just put it to the air differently.

Simply put, the 4200Kv motor will spin a smaller prop at a higher RPM on the same Volts and Amps as the 3700Kv, either direct drive, or with the same gear ratio. You can fiddle with the gear ratio and get both motors to spin the same prop at the same RPM on the same Volts and Amps.

What simplifies this is the fact that you can't get just any gear ratio, and in the case of the MiniFuntana/MiniEdge, you get a workable 6.6:1 gearbox with the plane. Sure, you could use the 4200Kv motor with the included gearbox and prop, and sure, you'll have gobs more power, BUT you are also pushing the motor well beyond its limits, drawing too many Amps, and something's gonna burn out sooner rather than later.