Here we are. Relievers have outperformed their FIP every year since 2002, and their FIP has outperformed their xFIP every year as well (Fangraphs only has xFIP from 2002 and on).
http://www.fangraphs.com/leaders.aspx?pos=all&stats=rel&lg=all&qual=0&type=8&season=2013&month=0&season1=2002&ind=0&team=0,ss&rost=0&age=0&filter=&players=0