The fx official temp is 62°C, but that's impossible to measure accurately and doesn't translate well on mobo's. It'll translate to roughly 75° on the cpu temp.
That said, there's no stopping that cpu, the FX9590 is the exact same cpu, but with different internal voltages and a 4.7-5.0 stock clock. So go ahead and try, if you want, there's no harm, take it as high as you can get stable on that 1.38v, AMD's max voltage for that cpu is 1.55v.
If you have any doubts on safe temps, use AMD Overdrive. It reads the Thermal margin, not the actual temp as such. Meaning it'll give you how much temp you have left. The closer to 0 you get, the hotter the cpu is running. At 0 or in negatives, you are over the cpus limit and now well into damage causing heat. So try to keep thermal margins well above the teens.
Just be aware, the hyper212 is a budget cooler, and as such reaches its limits quite quickly once it gets to a certain wattage output.