@VanijaDev Manual is definitely the way to go, otherwise your temps will be much higher and you could run into stability issues when overclocking. I've had all my open air MSI RX480 rigs set at 65-70% fan speed mining for over a year with almost zero downtime, and the temps never go above 60 degrees. Usually around 55 average. My single 1070 is another story, but that's only because it's a founders edition inside a case. My 1070 fan is set at 85% with the power limit at 90% and it runs around 63 degrees.
Keep in mind that anything below 80 degrees is considered safe, so it's not necessary to target such low temperatures, it's just my personal preference. You might find you prefer silence rather than lower temps, so you can adjust your fan speed accordingly.