I love my 20° Incubator, and I've only just started really getting to grips with rigging it for maximum warmth. There's never really been a question for me that my next purchase will be a Burrow.
It will replace an old Kathmandu sleeping bag that is rated as follows: limit of -10° C (14° F), and a 'comfort' rating of more like -2° C (28° F). It's 700 loft duck down as opposed to the HG 900 goose down. It's been a pretty good workhorse, but I was staggered to discover I could save about a kilogram (2.2 lb) of pack weight by switching to a dedicated top quilt. Sold!
My dilemma is, I'm not completely certain whether to opt for the 0° version. On my recent winter trip out the sleeping bag opened (except for the feet) was insufficient on the colder nights, but fine if I put the whole thing on and zipped it up completely. I guess it just creates a tighter envelope, even if the layer underneath you is compressed and not too useful. This is on frosty nights, but with no actual snow on the ground, and not too much wind chill. It's probably going to be unusual for me to be hanging in snowy conditions.
I can't really afford a quilt for every season. At least, not yet! I'm starting to think getting the 20° F version with 2 ounces of overstuff would be a good compromise... an improvement on what I have, but not so insanely hot that I can't use it with the snaps open on warmer nights?
Also, I'm right in thinking that if I have to go to ground, a Burrow + pad is fairly equivalent to a similarly rated sleeping bag + pad? For us taller blokes, is it worth asking for one or two snaps higher up on the quilt to help keep the edges in?