1. Applying thermal paste. (of course, if you haven't already done so)
2. If you have applied thermal paste, make sure its done correctly.
3. If all the above has been done correctly, but temps are still too high, then you will need to lower the clock & voltage of your cpu.
If the cooler cannot handle the cpu's temperature then it starts to become a bottleneck. If you want more horse power out of the cpu, then you will need to grab yourself a better cooler.
Try using better thermal paste like arctic silver 5 or prolimatech PK-3 and re-seating the H100. I have a similar set up on one of my AMD builds and had tons of issues getting the cold plate to stay put. The mounting system for AM3+ is just harder to deal with; as the cold plate of the CPU cooler tends to move around you really need 3 hands to install the cooler properly. My advice get someone else to hold the cold plate down while you put in the clips and screw it down.
As long as you keep the temps under 60c-65c (prime95) you are doing well. My 8350 is able to overclock to a healthy 4.8 Ghz stable 24/7 overclock with a H100i at 1.465 volts. (only ever so slightly better then your cooler) Also keep in mind that not all processors overclock well, AMD has more consistency then Intel, but, sometimes you do lose the silicon lottery.