watercooling

hi all,
at the moment i have a maxxxpert watercooling system, and its been great.
however, my case needs have moved on, so a new case will be bought and new
pipe has been bought - from 6mm ID to 1/2" ID. also some new connectors have
been bought ready for the new case.

however i`ve temporarly moved to air cooled cpu so i can swap watercooling
connectors to barb 1/2". i`ve just released the waterblock connectors and
there 1/4" thread, not 3/8thread as i thought&planned for.

so i`m now going to have to re-order some 1/4" threaded barb's.

question is, will the 1/2" to 1/4" restriction impinge cooling drastically?
if so, can only recommend me a waterblock? i`d prefer the waterblock to be
all metal and preferably use the sockets fixing device, not the 4 holes as
most use.