I remember reading a thread somewhere (maybe not even on this site) with a bunch of math in it that showed that Climashield was at least as warm as down, oz for oz, that was before APEX. The Climashield required far less loft than down due to it having better thermal resistance properties. Climashield fibers are hollow. Loss of loft will most certainly effect warmth but not proportionally, as it would with down.
Down is still king for being compressible, so if size is a factor...
I do most of my camping by canoe. I've been on trips where it rained for several days in a row. I can afford some bulk for the security of knowing that if things are damp I still won't freeze.
BTW Besides requiring more stabilization, Primaloft will not hold up a well as Climashield.