I've been looking into this as well to extend my winter sleep system, so I'm interested in hearing others' findings, experiences and tips/tricks.
I've got a 15F Katabatic down quilt which keeps me comfy down into the teens with just base layers on. I can push it a bit more by wearing my insulated clothing, but I'd like to be able to extend my system comfortably down to around 0F.
I've been leaning toward achieving this by pairing a light synthetic quilt with my down quilt. The synthetic would help with moisture management (both from condensation and perspiration) in addition to providing some extra warmth. The synthetic quilt could also work stand alone for the warmest of overnight trips in the summer/fall.
I've been looking at the EE Prodigy Quilts in the Reg length/Wide cut; either the 40F or 50F model. I'd appreciate some input from others on what temp rating I should be looking at for the syn quilt; I'm leaning toward the 50F at the moment as I already have another 30F down quilt, so this syn quilt would only be used in combination with another quilt or on its own for those warm summer trips.
I'm also interested in hearing any experiences or advice on how best to attach the quilts or otherwise keep the syn quilt in place on top of the down quilt.
Finally, I assume one needs to size up on the synthetic quilt to fit over the down quilt. If I'm using a regular width and length down quilt, is sizing up to a wide width syn quilt sufficient?
Looking forward to hearing what others have to say. Sorry for the slight, but related, thread hijacking...