Also, if you're on a molex connector, you can get something like this and use the 5V instead of the 12V connector.

http://www.acousticpc.com/zalman_multi_connector.html

Definitely avoid H70, it has the same pump as the H50. Thanks for the resistor link.

Maybe my tolerance level has gone up, but my H50 pump noise is acceptable. Fitting an H50 with a push-pull pair of Nexus 120mm fans (on silicone gaskets & plastic tie-wrap connectors), the pump plus 2 fans gives me the same moving-parts count as the CPU fan, 90mm case fan, and 120mm case fan. But it is much quieter than the old setup, and reduced CPU temps by 25c idle & 35c peak.

The pump & fans are each connected to their own mobo connectors thru their own Zalman fanmate 2's; they all seem to work fine at any speed, including the pump. The pump is much quieter when turned all the way down, and it is still turning.

The H70 radiator is thicker and has more tightly packed fins. You'll need more fan force (& more noise) to get the airflow you need vs the sparser H50 radiator, especially at idle, which is when most of us notice noise the most. If I needed more cooling surface area than the H70's 120mm sq, I'd probably get a 120x240 radiator instead of the Corsair self-contained setup.

Then again, this setup is in my 3U core i7 SBS 2008 server. Not really trying for "silent" so much as "quiet 'n compact" while the build is in server mode.