I found the solution to my mosfet heatsink issue...throw it away!

After 3 hours of burning in at 1.55 volts and 3.8 GHz, that top heatsink was just warm, the top edge of the MB was rather hot, and who knows what that heatpipe thing was doing in regards to cooling that area. After that burn in, I took the heatsink assemblies off. On the mosfets the heatsink tape didnt melt in much at all. Only about 50% of the mosfets made marks on the tape. As the heatsink was doing double duty as an airflow killer while not really helping with cooling, I just took them off and am not going to worry about it too much. If anything, removing them might actually help cooling in my application. I have 2 120mm fans blowing down onto the MB, should be better than with that sort-of heatsink the board comes with out of the box...