What class are you running in, BSP, street tire?
Check out this post, there is some good info in it that goes with your questions.
SCCA STR 370z Progress Thread.... It can be done!
Here is a thread I started about sway bars.
Sway Bars, Track and AutoX?
This last year pulled considerably better times on Swift R spring then I ever did on the Nismo springs. (yes spring changes are illegal in BS, but ssshhh) Still came in 4th over all so it didn't help to much.
I ran BS in my Nismo last year and I'm moving up to ASP this year.
I hope that is some help, good luck!