read lots of reviews online, there antartica CPU block seems pretty good, between most CPU waterblocks theres not a lot in it, couple degrees across the range, with the storm, apogee and the likes at the high end and the zalman, asetek and the likes a bit down the range, a few degrees won't kill your ability to overclock, cause with water you should never get temperatures high enough to be worrying

i personally use the following:
Stealth GT 240 Rad. W/ two 120mm Aerocool Turbine low RPM fans
Alphacool Cape 20 Res.
Alphacool AP1510 Centrifugal Pump (expected it to be loud but was suprised)
Swiftech Apogee CPU Block
Two Danger Den Maze5 GPU Blocks
Polarflo TT GPU Block cooling chipset
Alphacool ASUS mosfet block
thats the order the loop is in as well, use tygon 3603 1/2" tubing, seems to work nicely
