Intel sells the "K" versions with the intent that they have their multiplier increased.
How high is variable so Intel can't guarantee any particular level.
You are safe so long as you do not go wild on high voltages.
I have become a bit jaded on the subject of haswell cooling for overclocking.
How high you can OC is firstly determined by your luck in the bin lottery.
I had high expectations from the Devil's canyon parts and their better thermals.
I found out that the thermals really do not matter unless, perhaps, you are a competitive overclocker.
Haswell runs quite cool, that is, until you raise the voltage past 1.25v or so.
Once you go past 1.3v, then you really do need very good cooling to keep stress loads under say 85c.
But, the consensus is that voltages higher than 1.30 are not a good thing for 24/7 usage.
I have been unable to find any official Intel recommendation on what is a safe vcore limit.
If you are an enthusiast, you can go higher.
Even if you can handle the heat, how much do you really need that extra multiplier from say 4.4 to 4.6?
My thought is that it is better to use the exotic cooling funds for a quieter and less expensive air cooler.
I suggest a good tower air cooler like noctua or phanteks with 140mm fans.
I stress test with OCCT.
It will monitor temps and vcore. It will shut down at 85c.
Just gradually raise the upper limit on multiplier and leave all else on auto.