Republican appellate court justice David K. Overstreet will join the Illinois Supreme Court next month after defeating Democrat Judy L. Cates, his colleague on the 5th District bench.As of press time, unofficial results tabulated by The Associated Press show Overstreet secured 62.78% of the southern Illinois vote to Cates’ 37.22%.Overstreet fills the seat being vacated by Justice Lloyd A. Karmeier, who was elected to the high court in 2004 as a Republican.Overstreet could not be reached for comment.Cates, a former …