3 to 4 psi on an auto will be fine. Probably even higher will be fine. I rode with a guy from TSN in his SL with the Twistec kit at 12psi on an auto. It lasted until he screwed up his engine, but that's beside the point.
3 to 4 psi is a huge improvement. I'm running 2psi right now simple because I'm too poor/lazy to work with fuel management and if you don't think 4psi is going to be worth the time and effort, take a look at these. Obviously nothing special and nothing like a 9psi setup, but you'll get the idea:
http://www.xwarlordx.com/vasceria/videos/SHI TS****EDUP.wmv
(remove the space) http://www.xwarlordx.com/vasceria/videos/MYCARSUCKS.wmv