I'm aware it couldn't overclock, hence why I purchased the K version.i7-6700k doesn't have stock cooler,
i7-6700 does, but i7-6700 - doesn't support overclocking.
Dark Rock Pro 4 is a good option.
Other options (but they are all pricey):
Cryorig H5, H7,Noctua NH-D15, NH-U14S.