Well, this thread is about a progressive spring, I wouldn't be talking about getting one if that wasn't what I want... Yes, Swift are the best linear, but I have no intentions of tracking the car hence why the progressive rate, which DO help a little with handling over stock, just not as much as a linear like Swift... Have you tried to race specifically with Eibach before?
The progressive rate works if you start at an acceptable rate. 90lbs-in is not one of them. Its too soft of a start point. You lose quite a bit of turn in to start then it increases in rate so fast that you go from grip to push instantly. If they started at the factory rate and increased to 210-220lbs-in this would quell the body roll, not increase it. You might gain a little bit of mechanical grip starting at the softer rate but lose it once the car shifts the balance to that tire. This then increases push to the point of upsetting the car.
I have tried every tire pressure setting i can in the back to quell the understeer and get more rotation. I think Eibach went too soft up front trying to increase mechanical grip while also alleviating the main complaint with the factory suspension(the rough ride).