Hotchkis TVS for A-Body's!

Summit racing has the kit for $1852.99:
http://www.summitracing.com/parts/HSS-80113/

The issue I was wondering about was the leaf spring rate is 130lbs/in, That is 30lbs/in less than the SS Springs. Any spring people know why this would be better?
The spring design looks nice being CNC'd bent, 1" lower stance, and rounded bends at the end rather than straight to the eye.