Robert,

From Amitron website:

" Non-Conductive fill has a thermal conductivity of 0.25 W/mK whereas Conductive pastes have a thermal conductivity anywhere from 3.5-15 W/mK. In contrast, electroplated copper has a thermal conductivity of more than 250W/mK.

So while Conductive via fill can offer needed conductivity in some applications more often than not it is possible to use non-conductive paste and add additional vias. Often this results in superior thermal and electrical conductivity with minimal cost impact. "

Recall reading a more complete paper on this somewhere but can't locate it right now.

More ammunition for the idea of using many smaller VII non-conductively filled vias and calling out increased minimum hole plating (Class 3 hole plating).