What parts u have already? PSU? GPU? OC not necessarily means vastly more power requirements, it depends are you overvolting or not, if not then power draw is hardly any higher. You can have a decent cooler for 30$ which would certainly be able to keep both K versions near 4Ghz with no hassle.
Aftermarket cooler is a good addition to stock ones anyways even if its not about temps it's far more quiet.
So give us a look over your parts and and number of $ you are about to spend, we might get something really good looking here.