I personally haven't used the CG Heavy clay bar, but I have used Meguiar's Mild Proffesional Clay and it works pretty good. They also make a clay that is specific for overspray (Meguiars C2000 Body Shop Professional Overspray Clay, 4 oz Mild) That's the link to it. As for the lubricant any quick...
I would personally wet sand them. Depending on how bad they are, I would start with 1500 grit and work your way up to 3000 grit. Next use a Rubbing Compound. Then I would use a finishing polish. Last I would apply a wax or sealant to keep them protected.