Intel’s Skulltrail enthusiast platform running at 5.0 GHz
 

Integrating the Seaburg chipset as well as two 771-pin “special” Xeon sockets, Piednoel told us that one of these systems has been overclocked in his lab to 5.0 GHz stable, and 5.2 GHz nearly stable. That system uses vapor cooling. The analyst mentioned he's using regular bathroom silicon around key parts of the board to keep condensation from becoming an issue. During Fall IDF he had a similar machine running just under 4 GHz with known BIOS limitations at that time which were keeping it from clocking higher.

http://www.tgdaily.com/content/view/34636/135/