Just pointing out that the sound tests show something different. Larger aio's can be more efficient by a few degrees, they're not custom loops though. If aio's were quieter they would show lower dba in the noise tests. The h100i gtx being the latest version of the pretty popular h100i dual fan aio runs louder than over 15 air coolers at idle and ranks near the bottom at full power. 30db louder at full speed than a noctua nh-d15.
It would likely depend on the fan curve, the aio's shouldn't have to run full out. At least I wouldn't think so, my larger air cooler doesn't even spin up with an oc'd i5 under p95 unless I turn off all my case fans.