For the final fan test we attached the blue Noctua ‘Ultra Low Noise' Adapter which Noctua rate at 7.9dBa for this fan. The fan slows down to around 1,000rpm.
As expected temperatures rise by another 10c or so on the processor while the Sapphire card temperatures increase by another 1c under load. These are still well within safe parameters and we can't even tell the system is on.
Again we had to hold our breath and maintain still movement to get our final measurement of 16.2dBa. Obviously the PSU and other ambient noise is adding a little to our reading but this was as low as our equipment was able to measure in this room. Even with our ear to the chassis we could hear nothing at all. The Silverstone PSU is clearly also very effective.