Efficiency
The 84.9% efficiency of the BFG ES-800 is the best result we have seen so far. BFG's Frequency Conversion Technology sure plays a big role in that.
Fan Noise
Above graph clearly shows how the PSU ramps up the fan speed with higher load. Unfortunately the acoustics tends to be louder than other power supplies offering similar capacity. Still, the PSU is very far from noisy. In any enthusiast system there will be other fans that will certainly be louder than the single 138 mm fan of the ES-800.