2x8GB is potentially faster when the need for RAM is less than 4GB, because of the dual channel. 1x8GB is more upgrade friendly.
What I meant was 2x4GB is potentially faster.
What do you get without the Killer thingy? Because the networking I get on default for my HP Pavilion G6 2131so is plenty good.
Also, go for the cheapest quad core. Not good for heavy encoding or compiling. But that is what you have a workstation for. Or at least a desktop.
For gaming upgrading from a generic quadcore is not going to give much of a perfomance boost. There are a few games with a ton of projectile calculations that benefit from CPU power and probably some other ones too, but most games rely heavily on the graphics card and not so much on the CPU.
Here is an example:
Inside the second: Gaming performance with today's CPUs - The Tech Report - Page 6
