I have my temperature target at 52ºC now that I'm mining eth only on rx580 (35% is the minimum fan speed possible) 1200mhz @ 875mv

GPU0 t=52C fan=35%, GPU1 t=51C fan=42%, GPU2 t=51C fan=35%, GPU3 t=51C fan=40%, GPU4 t=50C fan=34%

For 24/7, I would avoid having anything above 70ºC because of the known failure rates of amd gpu's