Puget Serenity is very similar to what I have built myself, and I can vouch for its silence.
I have the Antec P182 case, which has 2 front fans, 1 top, and 1 rear.
I also have an Asus motherboard with Q-Fan support. This one is the most important as it controls all the fans in the computer and keeps it silent on idle.
My GPU is the Nvidia GTX 560 Ti (Overclocked + Overvolted) which I personally replaced the fan with the Arctic Accelero fan. The stock fan sounded like an airpane taking off
. I absolutely cannot hear the aftermarket GPU fans on load and the load temps are very low. In fact, the noisiest part of the computer are the case fans which are virtually inaudible.
Hope this helps you in your quest for silence!