4770k should handle the 1080 no problem* at stock and oc'd
your psu is way more than needed for a 1-2 card setup, especially for the 1080 which uses about half the power of a 980ti.
typical load for a single 1080 build will be around 300w, so with a 1200w psu you would have more than enough grunt to run a 2-3 card build you wanted.
6+2pin is an 8 pin connector mate. so no need for a new psu either.
*i have seen 1 site (gameers nexus) claim that the 1080 is bottlenecking even higher end cpu's.
but they are referencing a particularly buggy game engine (warhammer total war) in there results so it may well be that the game itself is the cause of the bottleneck and not the hardware.