With the original staggered setup, the wheels can't be rotated to even out tire wear. This is a big minus as the front and rear tires wear quite differently. This can be solved by using the same rim and tire dimensions front and rear - a square setup. The wider front tires also improves the front end grip and shift the chassis balance rearward, which I prefer.
The 14" Wilwood Aero 6 brake kit requires 18" inch wheels, and are known to fit behind the C5Z rear rims. I was fortunate to get two OEM rear Speedline C5Z rims from House of Wheels at a good price, in the same finish as on my car (there are variations in color). They even survived the long distance travel from the USA to Norway without any dents. I have to issues with this configuration, no wheel arch or liner rubbing. This is how GM should have configured the C5Z.