PC case makers typically list the maximum cooler clearance on the case's spec sheet—check it if you're air-cooling. (More on liquid-cooling in a moment.) Most towers won't present any problem ...
You can save some money and pick the NF-S12B redux-1200 if you are solely using these fans for your case cooling. However, I do like the flexibility in the redux-1700 for about a dollar more.
Your case fans help your CPU cooler disperse heat from its heatsink and bring in cool air to keep the internals at a safe temperature. They aren't powerful enough to directly cool a CPU. Think of fans ...