Your overclock potential is determined by how lucky you are in getting a good chip.
As of 6/19/17
What percent of samples can get an overclock
at a vcore around 1.4v.
I5-7600K
5.3 samples exist, unknown % of occurrence
5.2 16%
5.1 27%
5.0 52%
4.9 72%
I7-7700K
4.9 83%
5.0 62%
5.1 29%
5.2 6%
Essentially, the same performance per core.
If your need is for more than 4 threads, the I7 is better.
Most games can only use 2-3 threads effectively, so the lower price of the 7600K might make it better.
In either case, the limiting factor is the vcore you need to use..
It is the vcore that generates heat that must be dissipated.
If you have a well ventilated case(two 120/140mm front intakes) then I think air will do as well as any AIO.
Here is the TDP suitability chart from noctua.
Both 7600K and 7700K are 91w TDP processors. Add some for basic or max overclocking.
http://noctua.at/en/tdp-guide
A NH-U14s or NH-D15s will satisfy your needs.
In the process you will have a simpler, quieter, less expensive, and more reliable cooler that will never leak.
And... such an implementation with front filtered intakes will keep your parts cleaner.