I'd recommend a bag filled with Climashield HL, which lofts very high per fill weight AND retains its loft over time and repeaded stuffings better than other synthetic fills.
My early experience (in the late '90s) with Primaloft was very disappointing due to its rapid and almost complete loss of loft in a well cared for sleeping bag. Their fill has improved over the years but I am still wary of its loft durability. It is a short fiber type fill and can clump. Climashield is, like Polarguard, a continuous fill, which is why teh military chooses it (Polarguard) for their bags.