Like any time you try to correct something on paint, you want to progress from the least to the most aggressive. So, I would start with a mild bar like the Clay Magic blue. Make sure to use lots of lube. If that does not do it, then move up to the Clay Magic red. You will mar the paint with that bar, so be ready to polish or compound afterward. If the overspray is nasty, it's not like you've got a choice anyway. Depending on what type of overspray it is, I would also try a solvent to get rid of it. That may work if it's fresh.