Mackan wrote:1) Is it safe to say that with the right components, the R5 case would be the most quiet build possible?
No: but it will be among the quietest.
Mackan wrote:2) When you talk about 14dB SPL, is that basically inaudible?
Broadly speaking, no: in the middle of the night I am able to clearly perceive things like this, which is rated 12dB. But you'd better define "basically".
Mackan wrote:Is there any mATX or minITX build/case that can compare with this R5 build, in terms of noise?
No, at least, nothing as small as a Sugo SG05 (whether we're talking about high power discrete graphics). Take note that the Sugo SG05 has been reviewed by SPCR a while ago.
And take also note that mostly depends of the enclosure placement (to say, right on the desk, at 30cm from your nose, even an R5-build might be heard).
Maybe something like a Define Mini or a Nanoxia DS4 could be among the quietest options available, as well as the R5, but they are just a tad smaller than an R5, nothing serious.
Eventually: a nice sound signature is way more important than the unobtainable physical inaudibility, the right signature let a build noise to disappear. Hope this helps.