New build, new concerns (can't test for 2 weeks) -

[MiRai]

I'm wondering if it would be better to go ahead and replace the 6-core with the 8 core intel cpu - thoughts?

If you can afford the 5960X, then get the 5960X.

I'm leaning towards 3 GPUs, only because it sounds fun and maybe later on with windows 10 it might scale better then it does now.

Using three of those GPUs in SLI is going to run terribly hot since they don't pull the hot air out of your system, and they just dump it out onto the next GPU over.

Motherboard.. yikes.. I have no damn clue now. Do they need to be watercooled for higher overclocks still? D;

I don't know of any motherboard that has ever required water cooling to overclock the CPU. Water cooling is also unnecessary in order to overclock a CPU unless you're pumping a bunch of voltage into the chip, which then causes a lot of heat that needs to be dispersed.

Any recommendations on a MB that can take 3 gpus, 8 core cpu, m.2 SSD and a soundcard..while being decent with overclocking?

Most X99 motherboards are going to support everything you want, so pick one that has pretty colors and matches your build.

Do I need a dedicated NIC for when I max out my cpu (15 box, streaming etc) to offload some of the work? e.g Killer NIC

No, but a shitty modem/router can cause issues with lag and disconnects. However, I only know of people having issues with D3 and not WoW, but anything is possible.