FWIW...

The approximate change in spring rate sounds significant to me.

A full turn on the adjustment nut with stock bars = about 1/4" of lift VS
1/2 turn with the HD bars = about 3/8", which should be about 3/4" at a full turn...

By way of the limited comparative info, that sounds like close to 3 times the torsional resistance.

When linked to an equally resistant "spring", by way of the SFIFS...