The 3oz Polarguard 3D is rated by the manufacturer at 1" of loft. Ray Jardine more honestly rates it at .9". My experience is that the loft will quickly degrade on a long-distance hike to about .65", after which there is no further loft degradation. Thus a two-layer quilt will quickly degrade to about 1.3" in loft. In theory, this is only enough loft, for the average person, for temperatures about 50F.
Generally speaking, a down quilt will run about 8oz less weight, for 50% more loft (2" versus 1.3"), and 50% less space (500ci versus 1000ci stuff sack size) as compared with Polarguard 3D. This makes down sound like a hands-down winner. However, it is important to consider exactly what conditions you plan to hike in, before you rule out Polarguard.
Most of my hiking involves nights with temperatures above 50F, but with the possibility of temperatures as low as the 20F. What I do is supplement my quilt on cold nights with my synthetic insulated vest and either a synthetic pullover or down jacket, which brings the torso loft back over 2" (or even over 3" for the down jacket), which is adequate for temperatures down to 20F. So I don't see the lower loft of Polarguard as compared with down as a real problem, nor do I care about the extra space, since my pack is roomy. The extra 8oz of weight I consider a worthwhile tradeoff for the added safety of polarguard. Also, polarguard can be easily machine-washed and dried in case you stink it up somehow. Not so with down. This is an issue for me, since I am normally traveling for months at a time, with no easy way to clean a down bag.
I should note that my quilt is a modified Jardine style. Instead of the Jardine "gorget", which I found suffocating to use, I simply extended the quilt to 87" long (I am 71" tall), then sewed up the edges of the head end, to make a sort of "head pocket", but left 8" unsewed towards the middle of the quilt for a "breathing hole". The added length brings my quilt weight to about 27oz. The breathing hole works for either back or side sleeping. (For side sleeping, the quilt needs to be at least 48" wide at the head, in order to allow the breathing hole to be pulled down to face level.)
The problem with the Golite Polarguard quilts was that they were too narrow and hence their were drafts under the sides. Jardine fixed this problem by increasing his recommended quilt width and by the addition of "draft stoppers" (something which down quilt makers have yet to copy, for some reason). Also, Golite used very heavy shell fabric and otherwise overbuilt the quilts so they were much heavier than necessary.
Fanatic Fringe doesn't state their dimensions, but based on their weights, they are not particularly roomy. Their quilts are also missing two important features. First, the draft stoppers. Second, either the Jardine "gorget" or the "head pocket" with "breathing hole" as described above. Making the quilt long enough to cover the head is critical to making it truly warm.
It is my belief that synthetic quilts are still in an evolving phase, but that the synthetic quilt/down jacket combination will eventually become the rule among lightweight hikers, at least for 3-season use. Using a down jacket with a synthetic quilt seems a much better solution than using a synthetic jacket/pullover with a down quilt, which is a combination many people discuss on this forum. Even worse is going all down. It takes only one bad experience with down to make you realize just how dangerous the stuff can be. My only bad experience was my own fault (my pack cover leaked and allow the bottom of my pack, where my down bag was, to fill with water) but the reality is that I am not perfect and I do make mistakes. Down simply doesn't leave a safety margin.