I don't think watercooling the northbridge is necessary. On all three of my MSI duallies, I have taken off the standard NB heatsink, made sure there was thermal paste on it, then put it back on, without the fan. I am running all three without the northbridge fan at all. Two of them are running at 150 FSB, the third is at 133. No stability problems on any of them, so I don't think that additional NB cooling is really needed. I took off the fans because they are fairly loud and annoying. As long as there is a ~little~ airflow going across the NB heatsink, you should be fine.