I don't know what temps are good for that cooler without doing my own research but I get 59c (max under prime) and around 43-45c in games with the same overclock (speed, volts and cpu) with the NH-D14
AMD chips usually crap out at around 65c+ the 1090T's safe max temp is 62c to 63c, i would look at getting a better cooler or decreasing the clocks, you might be killing your cpu (if it hits 61c or 64c as you said, even if it is brief).
shouldn't i be looking at the core temps anyway not the cpu temp as this ios not a sensor in the cpu as my core temps are 54c at full load and by in taking air i can get below 50 just need a dust filter.