Wow, I can't believe I missed this entire conversation!
All good information here, but I just want to point out another option when considering your spring rates. Rather than going with high spring rates when I assembled my suspension, I went a bit softer (275/150) and made up the difference with swaybars.
My thinking in this is that the softer spring rates allow for a bit more compliance in keeping the rubber attached to the road. Too high of a spring rate, and you can get the same effect as a rock being skipped across a pond (the spring is so stiff, that the car can't absorb enough of the little bumps to keep the rubber on the pavement). I have actually seen this happening with a fellow competitor's RX7 that uses 450 Lb. springs on the front (not sure of the rear rate).
So, using a softer spring can make the car "stickier" and give higher traction. But softer springs will also cause more body roll, right? Well, that's where the swaybars come in. Running stiffer swaybars keeps the body roll to a minimum, without causing a (noticeable) increase in ride stiffness.
This setup has brought me great success in autocrossing in CSP, to the point that I am now beating the Miatas consistently (even those on race rubber Vs. my Sumitomos). And, even better, the car is perfectly capable of being driven daily on the streets. I even made the 800 mile trek down to Deals Gap last spring, quite comfortably.
So, there seems to be two basic opinions concerning spring rates. One is to go very high on spring rates, and sometimes even removing the swaybars altogether. The other way (like mine) is to go softer on the springs, and heavier on the swaybars.
I am very happy with the path I chose, and the car has been a real monster at the races. Anyway, I just thought I'd throw that out there for you to consider. Hope this helps.
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