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Spring Rates

I've spent a bit of time mucking around with a springs and shocks to try and make something from parts I have on hand to suit the new suspension setup. Basically I want to determine if I should use a set of coil-over bits and pieces I had lying around or cut and re-shape the std springs.

 After dong the maths on it(below) the aftermarket coil-over springs I had lying about are most likely going to be too stiff, being 28% stiffer than the stock springs. If I cut one coil from the std springs it will be 50mm lower and 20% stiffer which might be a good compromise. If I want to lower the vehicle further without having to buy new springs I could always lower the, lower mount.

The numbers: 
Part Dimension Value Unit
STD Strut Length 635 mm
STD Strut Travel 190 mm
STD Spring Length 345 mm
STD Spring O.D 120 mm
STD Spring  Coils 5
STD Spring  Wire Dia 10.3 mm
STD Spring  Rate 16.89 N/mm
STD Spring Safe Max Travel 158.63 mm
Less one coil Length 295 mm
Less one coil Rate 21.112 N/mm
Less one coil Safe Max Travel 126.9 mm
Aftermarket spring O.D 87.2 mm
Aftermarket spring Length 223 mm
Aftermarket spring Coils 8
Aftermarket spring Wire Dia 9.7 mm
Aftermarket spring Rate 23.548 N/mm
Aftermarket spring Safe Max Travel 166.3 mm
Less one coil lower than Stock 50
Less one coil % stiffer than Stock 20.00%
Aftermarket spring 28%
http://www.acxesspring.com/compression-spring-rate.html

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