Just going off the Haz PC Build For "Excellent-Best Overall" on the OP...
But a few questions
- Is this PC necessarily Quiet? I keep my computer on overnight a lot and I seriously don't Engines revving while I'm sleeping. I'm not sure what factors determine that but I refuse to use a water cooler since I screwed up and have nightmares to this day.
The main factors for noise are fans and HDDs.
Having built a decently quiet PC myself (not disturbing at 1ft on idle at night, barely audible at 6 ft., and basically inaudible at 10ft.) I remember looking at the Hyper 212 EVO and it was very good in terms of noise.
Here's a link comparing a large number of CPU coolers noise levels:
http://www.frostytech.com/articleview.cfm?articleid=2655&page=3
When idling, the Hyper 212 EVO outputs about 30dB, which is very quiet (47dB under load).
As for the HDD, it doesn't seem to be particularly noisy (the WD10EZEX seems to be around 30dB) so that should be fine. SSDs are completely quiet.
For the GPU, I'd advise you to read reviews with noise indications before you choose your brand. They're not all made equal in that regard.
PSUs can also be noisy (since they're equipped with cooling fans). According to Google, the SeaSonic mk12II can apparently be very noisy under load.
That said, CPU cooler, GPU cooler and PSU cooler fans are often fairly quiet under light loads, so they're not going to be your biggest area of concern during the night, unless you mine bitcoins like it's 2012.
The main thing I'd take a serious look at are the case fans, because these can be loud even when your PC is idle or under light load. Also, the more you have, the louder. So if possible, be sure to check how loud those sold with the case you're eyeing are. Fans bundled with good cases tend to be decent, but it's worth double-checking.
If you need, there are plenty of quiet case fans available. My case has some Zalman and Gelid fans that are pretty good in that regard.
Remember that basically, in order to achieve the same airflow, a small fan will need to rotate a lot faster than a bigger one, so whenever possible, use 14mm fans with low dB ratings.
Also, vibrations are a huge factor that's easy to overlook. Both fans and HDDs produce vibrations, and the noise made by those vibrations is greatly amplified by the case.
Using rubber washers on the HDD screws can offset that to an extent. Otherwise, there are extremely efficient casings you can buy to insulate drives (the only ones I know are the Smart Drive series by Grow Up Japan, but they're expensive and require you to put your HDDs in 5.25 bays).
For fans, the absolute best solution is this:
http://www.ainex.jp/products/ma-023a.htm
These are rubber fixations designed to replace screws on case fans and absorb vibrations.
I swear by those; they're night and day even compared to screws with washers.
In order to make your machine further quiet, one solution would be to add a 3.5 or 5.25 inch fan control array, which allows you to manually dial down fan rotation speeds. If you have enough large fans (120mm or preferably 140mm) and a case with plenty of room and air openings, chances are you'll be able to keep things decently cool inside even at very low speeds.
Then when you game, or do some heavy work, you can crank up the fans back to their normal rotation speeds.
Alternatively, you could also use PWM enabled fans.
They're a lot less cumbersome than manually controlled regular fans, but more expensive (and you'd most likely need to buy replacements for the regular fans bundled with your case).