echoing posh, look at fortue auto 500s. the next step down is BC BR. 19 wheels (not rims) will be too large for your car and track duties. stick with 17 or 18s. 'flush' and track cars do not mix.
i believe most IS coilovers come with a 10/8 spring rate. you would be surprised how soft that is for our cars. i have 12/10 and wish i went higher (my car is just for 'show' and driving around, no track duties). i recommend you reach out to fortune auto and BC and they can help you pick rates too.
Lucy; 04 manual sportdesign