I think you'd be better off with G/C. Even sportlines don't really have the kind of spring rates you'll want for autox. I have 400lbs front and 400lbs rear, and its still acceptable on the street with 15s (I would even consider it an improvement over stock, but I'm wierd). I think CivicSiRacer has 400f/450r, same body type as yours, seems to work pretty well for him.

I just don't think a normal "lowering spring" will satisfy you if you plan on racing a lot.