AMD processors had been overclocked at speeds up to 8.429 GHz

It has been published on  a blog post that the eight FX processors had been overclocked at speeds up to 8.429 GHz, beating the prior record of 8.309 GHz, using a third-party team of overclocking enthusiasts.
AMD's announcement opens the Intel Developer Forum here in San Francisco, a developer conference hosted by AMD's arch-rival and much larger competitor, Intel.

Source: www.thinkdigit.com