I have an '05 CTS with the 17" sports package, and it is about time to replace the tires. As long as I am going to invest in new tires, I am considering upgrading the wheels at the same time. After 2005, there were two options for factory provided 18" wheels, in 9-spoke and 12-spoke varieties. I was hoping your could provide model numbers for both as well as wheel and tire specs (i.e. diameter, offset, and width). And what would you charge for each option, wheels only for a set of four/five (just in case I want a full size spare)?