These are beautiful!! How do you do your HDRs? Mine always come out with the "overdone" look.
And I always find anything above f/4 to be just perfect for cars.
Example:
http://www.flickr.com/photos/jsitthi/3400762838/
Most of the time when I'm shooting events, I don't worry about aperture all that much. It's usually just luck through trial and error.