Kgf per unit are is pressue essentially which is stress when applied to solid.
In a hard impact the spoke can go slack and in those circumstances the radial stiffness will drop a bit. Increasing the spoke tension will mean more load is required to make the spokes go slack, it can't increase the stiffness of a wheel though. That is entirely determined in a tensioned wheel by the lenght of the spokes and the stiffness of the components. Those material properties are not effect by tension.
All pre stressed system are "stronger" than unstressed one think of heat treated shatter proof glass. The heat treatment put the surface in compression therefore a higher bending load is required to break the glass. The material properties of the glass are the same (or nearly the same) but the pre tension is the bit that gives it its toughness.
I had wheelset on rims kinlin xr200, Bitex hub, 28 spokes rear (DS 3x race, NDS radial laser).
tension was on DS around 120kg (parktool TS) - test rider (almost elite racer) noticed wheel is not very stiff (rubb in barekpads) - i put more tension on spokes (around 140kg on DS- parktool TS).
Wheel was noticebly stiffer-
So high spoke tension is need if powerfull rider wants the best from wheel.
But 140kg is too much for aluminium - it was test wheelset (and after 8.000km is still ok)