well I've done quite a few tests with a danner 700 gph magdrive pump which is rated at 60 watts. It transmits about 43% of that to water when inline and about 53% submerged ( 26 & 32 watts).
for more detail we have a thread going on about this exact subject over at the overclockers forum here:
http://forum.oc-forums.com/vb/showth...0&pagenumber=1
Sorry if I'm not supposed to provide links to other forums, let me know and I'll remove it.
-Sidney