12kg is REALLY stiff.

Here are the coilovers available for the 300zx. I know its not the same car but it could give you an idea of what spring rates certain coilover brands are.

Stock Springs for a 300zx:

Front:
3.0 kgf/mm (168 lb/in) Coupe & 2+2 NA
2.8 kgf/mm (156 lb/in) Twin Turbo

Rear:
2.2 kgf/mm (123 lb/in) Coupe & 2+2 NA
2.4 kgf/mm (134 lb/in) Twin Turbo


SPL (KTS)
15 levels of dampening adjustment - F & R
Front 8.0 kg/mm (448 lb/in)
Rear 6.0 kg/mm (336 lb/in)

Tein Flex
16 levels of dampening adjustment F & R
Front 8.0 kg/mm (448 lb/in)
Rear 6.0 kg/mm (336 lb/in)
Compatable with EDFC

Endless (Zeal)
6 levels of dampening adjustment F & R
Front 10.0 kg/mm (560 lb/in)
Rear 7.0 kg/mm (392 lb/in)

Topline Aragosta
12 levels of dampening adjustment F & R
Front 7.8 kg/mm (437 lb/in)
Rear 5.8 kg/mm (325 lb/in)

Megan Racing
32 levels of dampening adjustment F & R
Front 10.0 kg/mm (560 lb/in)
Rear 8.0 kg/mm (448 lb/in)

SPL-Spec Zeal Super Function Type-C
6 levels of compression dampening F & R
6 levels of rebound dampening F & R
(Total 36 way adjustable)
Front 18 kg/mm (1008 lb/in)
Rear 16 kg/mm (896 lb/in)


Plus thats a huge difference between front and rear. Now im not sure what coilover kits are like for FWD but it just seems really stiff