GPU temperature -> the lower the better (less leakage currents -> reduced power consumption)
fan speed -> the lower the better (cheap sleeve bearings...)
So I've recently put my rigs on the balcony, got me into the range of 40-60% fan speed and 30-50 °C GPU temp (before: 70-100% and 60-80 °C), reducing the total power (at the wall) by more than 10%.
People placing their rigs on balconies/outside have no issues with humidity (not to mention rain, etc.)? I was wondering if I could do that but it is too cold outside now (-18C at noon, up to -25C at night)