http://www.bulletproofme.com/Body_Ar...ml#Stand-Alone
Multi hit, stand alone ceramic plates are about the toughest thing commonly available. Rated to stop .308 and .30-06 armor piercing at about 2,850 fps.
A one ounce lead slug is a heck of a lot of mass to try to walk away from though, not sure how level IV plates are rated against slugs.