Primaloft is a great synthetic insulation and you are talking about nearly 6 osy. I would think that thickness would get you down into the low 20s, maybe even lower. (Depends on whether you are talking about Primaloft Sport or Primaloft One).

However I wouldn't use Primaloft for a sleeping bag or quilt. For large panel projects like that you really want a continuous filament insulation like Climashield or Polarguard Delta. Primaloft needs a scrim layer to stabilize it and that weight penalty can be pretty big for a large panel item like a quilt. For smaller projects like jackets I hear that Primaloft is good (I've never made an insulated jacket myself). In fact you might want to ask if the weight you are stating includes the weight of the scrim. That would make a difference.

You might want to check out what they say over at Thru-hiker

http://thru-hiker.com/materials/insulation.php

He sells Primaloft and Climashield and recommends the Climashield for quilts and the Primaloft for clothing.