I'd suggest downgrading the CPU (4x is enough and an Intel shouldn't overheat) and using the savings to go for an nVidia video card, as they will always have fewer compatibility issues with Cryptic games than ATI.
Yeah six cores is overkill right now. And as Sam said, Nvidia is a better choice for graphics card. And while the memory is nice you don't really need more than 4 GB. Make sure you get 64 bit OS to utilize it.