Agreed, a bigger supply just gives you more cushion for the future, and your usage will fluxuate more power when under heavy load less when you don't need it. But the psu is a transformer essentially and shouldn't take to much to power
I agree the 6700k is a great cpu, you could go 6800k if you want the x99 boards I believe some have 2 16x pci express ports (don't hold me to it though)
It actually does if care that your game runs smoother. Comming off of an xb1 I can tell a huge difference. First game I played was wow and averaging 190 fps is like eye candy