Either will do the job.
I have used a NH-D14 before, and it is very large.
I had a small problem with it touching the back of my graphics card in the first slot.
I highly suggest the newly revised NH-U14s.
It is redesigned with a slight offset to clear graphics cards and to allow ram with tall heat spreaders.
The NH-D15s is a bigger cooler, but I think not really much better.
Your odds of a 4.9 OC are good.
As of 1/13/17
What percent of samples can get an overclock
at a vcore around 1.4v.
I5-7600K
5.1 28%
5.0 52%
4.9 72%
One thing to consider is that you need to supply fresh air to a cooler for it to do it's job.
Something like two 120mm front intakes or better will do it.
I use a NH-U12s to get to 4.9 and my only intake is a...