C10 coilover spring rate for autocross

[vet57air]

I have a pro-tour 66 C10, I call it a Cgt. Has a custom frame to my spec to carry its 22's. I built it to handle and have been playing with coilover springs to fine tune the handling/ride height. Problem is from what I have read I am in a little uncharted territory. I started with 650# front springs with 500# out back. The rears are mounted vertically and I find them fine, mind you it is much more than I would expect, but it is not harsh. The fronts with the 650's I had the collars up showing about 2" of thread. They are mounted at about 70 degrees. I bought some 750's and to get my ride height have about 3/4" of thread. Driving the 750's feel much more compliant, not as hard as the 650's. Am thinking of going to the next spring, but it is a jump to 900#. Yes, I have used ridetech's calculator and my 750 is their "full on racing" weight. Anyone else using spring rates in this range or higher?