I presume you're using the coilover-conversion Vikings that use the upper spring cup in the subrframe (identical to the QA1 design)? These have a long spring, so 600lb/in is pretty huge. On my iron block turbo LS motor I used 450 lb/in springs for a bit on QA1 conversion coilovers, and they worked well but were a bit squishy. I would've changed to 500 or even 550's if I decided to track my car on a regular basis.
I see you are running a N/A aluminum block LS7 I would suggest 450 for a fun street car, 500 for street/track car.
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