I wouldn't have thought 600lb springs too soft - my Corse I has 450lb in the rear which I'm happy with from a ride/stiffness trade-off standpoint (this in on a way without anti-roll bars). I solved the issue of wheels hitting the bodywork in bump by removing (quite a bit of) material from both the arch lip on the clam and the inner arch area on the main tub until I got enough clearance. Now it's the damper bump stops that limit travel. This gave me roughly equal bump and droop distances. Otherwise either my ride height would have been off and/or very little bump and too much droop.