|Between 4x4 and 2x8, you probably won't notice much difference. In theory, having quad-channel (four sticks) should give you better speed, but in reality it won't increase performance that much. 4x4 would probably be cheaper, although if you only have 4 DIMM slots then you won't be able to upgrade without trashing some of the cards, which would be a waste of money. Personally I would get 2x8 just so I could upgrade in the future.|
Considering the hard drive is about $350 (on newegg), I would suggest downgrading to a 120 GB SSD (~$120) and get a large 2 TB HDD (~$120). Same price, about 8x the storage, and you could store OS and heavily used programs on the solid state for better performance.
Personally, I'm an AMD person, so I really couldn't tell you much about the CPU you chose. I will say this, I have an 8 core and I haven't seen one game yet that has needed more than 4. You could save a little cash by downgrading to a quad-core, maybe at 4.2 GHz or something.
After looking at the mainboard, I now see that it has 8 RAM slots, so you would be OK with either 4x4 or 2x8, just go with whatever is cheaper.
Just note, you could only put up to 8 GB cards in each RAM slot, as the CPU only can use 64 GB. Also note that the fastest RAM you could use would be DDR3-1866 because of the processor.
Generally, getting two separate cards would be completely useless, unless you connected them using CrossFire or SLI (AMD or Nvidia, respectively). In which case, it would probably be more cost-effective to buy two medium power, although cooling might be a problem.
First off, you could always get a cheaper motherboard, as I really don't think you'll ever need 8 DIMMs or 3 PCIe slots (unless you go with that SSD, it takes up a PCIe).
Do you have any thoughts about PSU or case?