It is a good question.
I have a Phenom II X4 955 box here running 8G RAM. Therefore I expect adding more RAM on the new box. Besides I will use the new box as virtual machine running >30 guests (VM) on it.
Now the old box Phenom II X4 955 is also a Virtual Machine running >15 guests(VM) on it, Linux/Windows. I have no idea if all guests are running at the same time whether RAM will be sufficient?
A folk on another forum suggested me turning to Intel i7 930