Looks like Intel may not be the only company whose next-gen CPU samples have, somehow, made their way into the hands of overclockers. Czech blog OBRovsky has posted what it claims to be screenshots and a video of an AMD Zambezi engineering sample overclocked to a blistering 5.1GHz.
A prior post on the same blog includes a photo of the CPU, and as far as I can tell, it looks legit. The words "AMD eng sample" and "© 2011" are apparently laser-etched on the heatspreader, and there's a full assortment of pins on the rear surface, which rules out a Socket FM1 Llano CPU masquerading as another chip. (Remember, Zambezi CPUs are designed to fit into existing Socket AM3+ sockets.)
The blogger assures readers that the Zambezi sample was "fully stable in Cinebench R11 @ 4,85 GHz! SuperPi 1M - 5,1 GHz on AIR," although he unfortunately decided to blank out the scores. Incidentally, his statement deserves some qualification. According to the attached CPU-Z shot, the CPU had to be overvolted to a rather intimidating 1.524V to reach 4.8GHz... and 1.596V to break 5GHz. While the processor was allegedly holding its own with an air cooler, that cooler looks to be none other than Noctua's NH-D14, which has six heat pipes, two fin arrays, and two large fans.