Earlier quoted context omitted.
> Big annoyance with SFF builds is noise. Not really any more. Most popular mini-ITX cases for enthusiasts support 240mm AIOs for CPU cooling. Noctua even has low-profile air coolers that fit in some mini-ITX cases and rival their biggest heatsinks in performance. The SFX PSUs are slightly more expensive, but the good ones are so efficient that the fans won't even turn on during normal (non-gaming) use. Modern SFF bu…
They do OK in noise-normalized tests, which are good for comparing and still relatively easy to perform. They're inadequate for quiet operation though. In fact the huge coolers I am using currently are barely adequate for their respective components - they require clearly audible fan speeds to avoid unhealthily high temperatures under sustained load. Certainly not extremely quiet; I'm not really happy with it, and I…
However, the modern SFF experience is much better than you give it credit for. An AMD 5950X with a 240mm AIO in a mini-ITX case is easy these days and it keeps the CPU temperature in a reasonable range.
But if your goal is a no-compromise quietest build possible, obviously you don't want to get a small case.
> plus it's rather expensive (more than 10x the cost of air cooling).
I'm not sure where you're getting these numbers, but modern AIO water cooling isn't that expensive.
You can get a good 240mm AIO cooler for about 1.5X the price of a good air cooler: https://www.amazon.com/Corsair-Radiator-Software-Control-Liq...