I am sure that you can guess the first thing that is different with the Phenom II X6 is the number of cores. AMD has dropped two extra cores into the Phenom II X6 to give you some extra computing power.
But extra cores is not the only thing that is different. AMD has also added in something similar to Intel's Turbo Mode. AMD is calling this Turbo CORE. This boosts three of the six cores by up to 500MHz to handle applications that cannot make use of all six. On the 1090T we used for testing this means that three of the six cores can run at up to 3.6GHz when needed to give certain applications a boost.
AMD also increased the amount of L2 and L3 cache; these have gotten bumped up to 3MB and 6MB respectively.
Luckily the new Phenom II X6 can run on either the AM3 or the AM2+ base with nothing more than a BIOS update needed to get things going. This means that you can run the X6 with either DDR2 or DDR3.
The Phenom II X6 is also still being run on a 45nm process with a die size of 258mm^2 (AMD should switch to 32nm next year). It also has a 125Watt TDP (lower than the original Phenom X4), it can run on voltages up to 1.4Watt and remain in spec, while the max temp it can handle is 62c.
So, it looks like there is not that much that is new. We wonder if the differences will be enough to get AMD back up to the same level as Intel's current generation CPUs.