99C5JA

Catbacks don't do anything for a C5 until you're making a lot of power. When I had just a filter and ran comparably modded Fbodies (filter/catback) the C5 was generally .2 to as much as .4 faster. Same day, same prep, same track. The gearing on the M6 C5 is the same as an M6 Fbody (3.42, same gear ratios in the M6). The taller tire (18 vs. 17) does gear it slightly higher. It's the C5 auto's that have the potential gearing disadvantage, 2.73 or 3.15 rear.

With the headers, you should definitely have an advantage and take him. As far as weight goes my coupe weighed just under 3180 with an almost full tank.