When you upgrade to larger sway bars, what is the net effect on stiffness?
When sway bar diameter is increased, stiffness increases to the 4th power.
This example shows an increase in stiffness of 24% for a 1 mm increase in diameter.
Note that this is for the bar only, and does not account for adjustment holes, end link length or tension, bushing material, or differences in metallurgy.
Tubular anti-sway bars are not covered by this formula.