I run mine on the firmest setting too. I have ran the bar in both and unhooked.
1. No bar. When I ran the car in autocross with no bar hooked up I found that it dives in a lot with a lot of under-steer. Driving it on the roads it felt real sloppy to me.
2. Softer setting. With the adjust-ability of my coil overs it felt a lot better on the street, and at the track under-steer was less but it was hard to predict when it would push.
3. Firm setting. I prefer this setting on the road and track. On the road I can adjust my coil-overs to a softer setting still giving me maximum stability with a decent ride. At the track I like a more neutral feel in the car by adjusting the settings on my car I can make it over-steer or under-steer with the throttle and brake. This setting provides me with my best times.
Hope that helps you out.