It depends on if you intend to do an extreme OC on air, or if you will settle for a sensible overclock.
CPU's vary and you never know exactly what you will get until you start to overclock it. My own i5 is good upto 4.3GHz, then the amount of voltage you have to apply to vcore, PCH, and ram gets silly.
I'm running i5 at 3.8Ghz on an Artic Freezer 7 pro REV2. It's a quiet and excellent solution, and leaves plenty of headroom at this speed once summer comes around and ambient temperatures rise.
The Noctua NH-U12P is for sure more effective cooling that the Freezer 7 pro REV2, but its a push-pull design, and it's huge. So you will have to check if you can fit it in your case, you will also lose a ram slot as the cooler will make the ram slot nearest the CPU inaccessible. From what iv'e heard, the Noctua, because of its size, is also a nightmare to fit.