"The Crosshair V Formula-Z is equipped with an additional 4-pin CPU power connector. While fitting it isn’t necessary, it can help the stability of high-level overclocks such as the one we’re attempting here. If your PSU doesn’t have one spare, don’t worry!"
http://rog.asus.com/216552013/crosshair-motherboards/guide-overclocking-fx-8350-to-4-8ghz-on-crosshair-v-formula-z/