Your board probably has SenseMI skew enabled, which is why you sometimes see temps below ambient. As noted earlier in this thread, the offset is not actually a constant +20C, it's variable, which makes reading temps even more confusing and inaccurate. My fan curve is also totally messed up - Low: 40C, Medium: 45C, High: 50C. There's about a 10C temperature range if you want your system to be quiet at idle and ramp up the fans at full load.
I have the same Phanteks cooler, and it's fine. I get about 64C Tdie running Prime95 Small FFT and the CPU boosts to 3.7 GHz. It throttles to 3.5 GHz running OCCT Linpack, which is normal and probably due to power/current limitations rather than temps, as Tdie was only 54C. If your CPU boosts to 3.7 GHz running Prime95 Small FFT, your temps are fine, whatever the readings show.