I just received mine and haven't put it together yet. I have the Koolance 601 as well. I purchased April 2003 and it's real quiet. The coolant according to the manual should be replaced once a year if cloudy.
The PC2-650 is my second water-cooled pc case. I will be using a Prescott P4-3.2E, Abit IC7-g Max 2 m.b, and Corsair LL twin matched pack of PC3200 memory(1 gig).
Some people out their have slamed Koolance because they use a small tube to carry fluid as oppose to others which have up one-half inch. Most of these people have probably never owned a Koolance or water-cooled system. I can tell you after one year of running, my temperature is always 30-32 degrees celsuis which is great and using the small tubing. My P4-2.8C is o/c to 3.5Ghz with stock voltage settings.
I have never tried to go any higher than 3.5Ghz. Plenty fast for me.