Actually the dual xeon HP xw4000 & xw6000's (passive/ducted)are nearly silent. I have installed 6 of them in small office rooms and do not "hear" increased noise levels over original pc's/mac's.
On dual xeons I have built here I use the Swiftech HSF with a variety of fans and always are noiser, but cooler. Tried variable speed with a Nexus fan controller - was a disaster - caused intermitant reboots when changing fan speeds (yes, I know of the reported issues with those).
Watercooled blocks are few, generally I don't like them.
My opinion...........
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