How far can I overclock an Intel i5 4690

Solution
You can get this CPU up to 4.5 GHz with the Noctua nh D15 (personal experience) at around 1.25 V-1.3 V, which should be plenty for you.
it is a k. Sorry haha forgot to put it.

 
My 4690k runs at 4.6ghz stable at 1.25v, 60c while gaming with a Cryorig H7 air cooler 32c idle temp. You should be able to get somewhere between 4.1 and 4.7 depending on chip lotto. It doesn't HAVE to be a water cooling system, there are plenty of air coolers that get identical temps to most of the AIO water coolers. But you will need some kind of aftermarket cooler.