Often with KW setups you can swap the springs out with custom springs via Swift or Hypercoil. I actually have such a setup on my car with KW V.3 albeit it's not a R35. Concept is the same and in doing so you can set your rates up to have optimum weight transfer. If you're not circuit racing then you shouldn't be worried of using a spring that the shock/strut cannot handle. Often those that are a little serious carry various spring rates for varying conditions.
Just some food for thought
I am not 100% on the cost of custom springs for the GT-R since I have not done such a setup but for my civic I paid $75 a spring. Relatively inexpensive and I cannot imagine a slightly larger spring which would be used on the R35 to cost much more.
There may be some need for helper springs to properly fit, but this is something where a call to Hypercoil or Swift would be fitting.
Rory