Hypercoil or Swift Springs w/o Coilovers
Currently on my E46 M3 I have Billstein HD shocks and Eibach springs. I bought the setup upon discovery that my factory rear spring had broken and at the time hadn't really thought about track-duty.
I am now getting my car ready for track-duty as a more primary focus (it's not my DD) and I'm wondering if I'd do well to upgrade/change-out the Eibach springs with a set of linear springs like Hypercoil or Swift?
If so, how do I go about selecting spring rates, length, etc?