How high you can oc a 6700K depends on your luck of the bin lottery.
Here are some statistics:
4.8 12%
4.7 47%
4.6 91%
And, no exotic cooling is needed. A simple tower type air cooler with a 120mm fan will do the job simply and quietly.
I am at 4.8 with a noctua NH-U12s.
In a nice case like yours, liquid is not necessary.
Liquid cooling is really air cooling, it just puts the heat exchange in a different place.
The orientation of the radiator will cause a problem.
If you orient it to take in cool air from the outside, you will cool the cpu better, but the hot air then circulates inside the case heating up the graphics card and motherboard.
If you orient it to exhaust(which I think is better) , then your cpu cooling will be less effective because it uses pre heated case air.
And... I have read too many tales of woe when a liquid cooler leaks.
google "H100 leak"