A group called LimitTeam managed to overclock AMD's Phenom II X4 955 processor and reach a record speed od 7.1 GHz.

A group named LimitTeam successfully overclocked AMD's Deneb 45nm Phenom II X4 955 processor (Black Edition) back on April 30, and submitted the results for validation to CPU-Z. During the process, the group used the Asus M4A79T Deluxe motherboard, dubbed as the Asus "multidimensional performance platform" featuring support for an AMD 140W CPU and the AMD 790FX/SB750 chipset. Additionally, the group threw in 4 GB of DDR3 memory from Apacer Technology and a ATI Radeon HD 4800 series graphics card. As a result, the group reached 7.127 GHz, beating the previous score of 6.7 GHz.
More at; http://www.tomshardware.com/news/AMD-Phenom-II-Overclocked,7747.html