Since you are on a different tire now, aren't all the old spring rates questionable? Surprised you aren't chasing rates similar to AI especially since you have plenty of options with shocks and valving. Sway bars are the final tuning point. If the spring rates and shocks are off, you are chasing your ass. Understand what the tire likes first and work back from that. Before we put a k member and watts link on Misty's Camaro it was basically a 500hp cmc car. Upping the spring rates netted nearly 3 seconds on an R6 Hoosier and kept the tires under the car. Going up in bar will only make the car have a narrow window if grip and less drive able. With the soft rates you posted and standard shocks, the car can barely manage weight transfer in any direction.