looks like your case is just a tiny bit too narrow for the better air coolers. If you want to try more aggressive cooling solutions as others here have suggested then I would try the Corsair H100i. you can mount the radiator to the top vents on the case.
No, you don't. The stock cooler will run fine. If you feel your temperatures are getting a bit too warm for your liking, then consider getting an aftermarket cooler then.
Stock is fine for cooling performance, as you can only overclock a tiny bit. However, if the temps begin to get too high or the noise is too much for you to handle, get a cheap aftermarket cooler.
looks like your case is just a tiny bit too narrow for the better air coolers. If you want to try more aggressive cooling solutions as others here have suggested then I would try the Corsair H100i. you can mount the radiator to the top vents on the case.