[pHaestus]

The only use I could ever come up with for heatpipes in water cooling systems was as a transporter and spreader of heat from small and/or inconvenient locations (VRMs; northbridges; inside PSUs maybe?) to external super low flow resistance blocks.

Otherwise the best case scenario would be that the heatpipe portion of your cooler presented 0 thermal resistance right? If that's the case then why have it in the way? And if it's resistance is more than 0, then why have it in the way compared to directly wcing the part? Perhaps if the heat spreading or suitability for running water to it are your primary limitations (see the examples I used above).