I've used the Comair Rotron 254mm in two of my WC setups. Quite loud at max power, but with a ceiling fan controller or similar, it can be near silent or at a happy medium. I've wondered about bolting it to the side of a mid-tower with a passive heatsink and running it at low speed, it would definitely provide adequate cooling for the whole mobo.
In my next WC rig, I am mounting my big Lytron rad with this fan in a window of the storage closet adjacent to my room so I can get cool outside air and run the fan at medium speed without any noise audible from my room. I'll drill holes in the wall and route the tubing along the wall to my comp. (Don't tell my landlord
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