Track Wheels, 16, 17 or 18"?

[mgfranz]

For autocross events, has anyone played with different rim sizes? I run 18" on the street, but was curious on others opinions. For autocross events, is there any big differnce between a 16,17 or 18" rim assuming the same diameter tire? I know that lower profile on a 18" would be tighter, but then the 16" with a 55 might give better roll. Thoughts?