When a lateral force is applied to the wheel rim, you have half of the spokes resisting it and the other half assisting it. Therefore, spoke tension doesn't really affect lateral stiffness. Same thing goes for torsional stiffness in a 3x wheel but higher spoke tension will result in greater torsional stiffness with radial lacing.

However, if you really want to pick nits, there is more strain per unit of stress at higher spoke tensions than there is at lower spoke tension with stainless steel. Within reason, the lower strain per unit of stress at lower spoke tensions results in a wheel with better lateral stiffness, i.e. a wheel tensioned to 100 Kgf will be laterally stiffer than a wheel tensioned to 120 Kgf.

I'll bet you a pint you couldn't tell the difference blindfolded though so don't take anything to extremes. On the bench in a lab, a wheel may measure really laterally stiff tensioned to 50 Kgf but it won't have enough radial stiffness to stay true.