350F & 250R spring rate...
so they lower the car 1.3" and barely add any rate up front (softer than a factory 1le spring) yet more than double the rate in the rear (to beyond almost any name brand spring for these cars)
I personally like a spring rate on the softer side for the rear of these cars, after numerous sets of springs. Here's a list of some rates just to give you an idea, my experience has been that linear springs ride nicer and feel more predictable in general over progressive springs
http://www.angelfire.com/my/fastcar/suspension.html