I find my 6600k stays very cool, I haven't over clocked it yet but during stability tests I struggle to get it over 50C and my fans are only just around 50% and that is only with the Noctua NH U9S cooler with 92mm fan. If you go for a big air cooler then air cooling should be fine, I think Skylake opened the door for air cooling much more then Haswell did.