https://www.ekwb.com/configurator/ in my experience, OC graphic cards may useful on GPU intensive workloads such as 3D rendering, the benefit in real world gaming would be higher FPS or maximum image quality setting, the down side is we force graphic card to use top power draw, = hotter = fastening life span expectation, the quicker part to be dead is GPU's fans, so water cooling is obvious choice at least two or three years later.
I recommend EKWB GPU waterblock over alphacool, watercool, aquacomputer, koolance etc etc base on the fact EKWB has (almost) complete full cover waterblock for various GTX 1080 variant.
Hybrid
If yours is Founders Edition then yes you can use CPU water block...