Don't know if it's been said already but I think you'll find that to run jap spring rates like all the fast jap cars you will need more aero to make it work.
I was at EC for superlap and the tomei/cusco WRX was crazy stiff but it also had crazy aero.
I'm still running jap spring rates (troy will know the exact specs) and I'm getting great times but I still think a slightly lower rate would be even better.
My 2c