Lance Hendrick is kind of the ice queen of coffee and promotes brewing and drinking at quite cool temps. He's said below 50C and even I think below 44C as recommended temps. I'd avoid over 60C at least. I think that's around the range where some data has even suggested higher rates of throat cancer with chronic exposure. Personally I now set my Ember at 123F (50C) which is about as low as I'm comfortable going presently. It is true that more complex flavor profiles tend to reveal themselves at cooler temperatures (closer to body temp - 37C)