AMD blogs that they hit almost 8.5HGz in an overclock a couple of weeks ago at their Austin campus. When I left the event they were approaching the 8.1GHz mark.

On August 31, an AMD FX processor achieved a frequency of 8.429GHz, a stunning result for a modern, multi-core processor. The record was achieved with several days of preparation and an amazing and inspired run in front of world renowned technology press in Austin, Texas. This frequency bests the prior record of 8.309GHz, and completely blows away any modern desktop processor. Based on our overclocking tests, the AMD FX CPU is a clock eating monster, temporarily able to withstand extreme conditions to achieve amazing speed. Even with more conservative methods, the AMD FX processors, with multiplier unlocked throughout the range, appear to scale with cold. We also achieved clock frequencies well above 5GHz using only air or sub-$100 water cooling solutions.