Your HSF is plenty capable of cooling an overclocked CPU. Just make sure to be very conservative about raising the voltage levels and you'll be fine. Your motherboard has an easy overclocking feature called CPU Level Up, but as many have pointed out ASUS is quite generous with the voltage to make sure those clocks can be reached. I would see what it's changing the settings to and use that as a starting point and then start lowering voltage in small increments until it's unstable and then bump it back up to the minimum voltage where it is stable. Get Prime95 to stress test your system for stability. You should be able to get 4.4-4.6 GHz without much trouble. Don't try to force it to do 5GHz, that's where you'll start running into problems that can cause damage to your CPU if you aren't careful. Very few people have an Ivy Bridge chip that can safely do 5GHz or more on air cooling.
Intel Core i7-5775c, Asus Maximus VII Formula, Win 10 Pro
EVGA GTX 1080, Corsair 2x8GB DDR3-1866, Corsair AX860
Corsair H105, WD Red 4TB x2, Creative X-Fi Titanium HD
Samsung 850 EVO 1TB, ASUS ROG PG348Q, Corsair 450D