About the springs- the change brought the 'spring frequency' up. The green/blue combination must have not kept those tires sticking to the clay. Does seem contrary to what 'text book' says. Most stuff says if you want more traction use a softer spring. Obviously there is a point where you can go to soft.

Funny combination on tires to me. We like a Bar Code style on short course at the indoor track here in KC. Most guys run Bar Codes all around. I usually go to Double Dee's in the front come main time. Why? Bar Codes give me to much steering. Double Dee's are more forgiving for me. Sometimes traction is so high I'll traction roll with Bar Codes on front.

I have never driven on a clay track. Sounds like you've experimented enough to know the right tire combination. Something else to factor in is the temperature of the track. I mostly race indoors in the winter months.