As with most of my miners and other computer related circuit boards, my personal experience has shown the upper limits to be an average of 74c. Anything higher and I start seeing erratic behavior including lock-ups and shutdowns. Operating higher than 74c-75c and you run the risk of damaging your equipment or at the very least shortening it's lifespan considerably. My personal preference is to keep everything in the range of 67c-72c with short term spike limits of 73c. This works for me.