IRWIN, I don't know what kind of racing you are doing, but for drag racing, I'm sure a smaller diameter wheel would improve your ET's.
Just for the record, Motor Trend's Dec 2003 issue had a comparison road test of the Crossfire and the '03 Mercedes SLK. Both cars were automatics, and mechanically identical. Even though the SLK weighed 70 lbs. more, it still ran the 1/4 mile in 14.84 sec. vs the Crossfires 15.18. The only reason given for the better performance was the smaller wheels and tires, and less unsprung weight.
The diameter of the SLK's rear tire had to be the same as the Crossfires because they were both turning 2,250 RPM's at 60 mph.
The SLK had 205/55-16's in the front, and 225/50-16's in the rear.
Both cars use the same brake and hub assemblies so the SLK's wheels should go right on a Crossfire.
Even with these much smaller wheel and tires, the SLK still had a .03 wider front and rear "track" than the Crossfire too.
It probably goes without saying, the Crossfire ran a much better slalom than the SLK, 66.0 mph vs 62.8, and pulled a 0.87 vs 0.81 on the skidpad thanks to it's much larger tires.