The Grand Master recommends only lightly upgraded springs, with stiff struts and upgraded swaybars.
Pretty good discussion
here. And, one thing I've found is that most makers do not want to reveal the spring rates or spring rate curves or whatever of their "street" springs. If you're buying a linear race spring, you spec it to what you need, but their progressive springs are carefully crafted for certain ride qualities yada yada yada.
