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%.