John,
My date and I sleep under a Dual Arc with tonsil, and consider it a value.
The BCB would not be large enough for us, especially in mid 20F temps. We are 6' and 5'7. The Nunatak website indicates 2.5 " baffles are used in both. Our microlight version Dual has a couple ounces of overfill, and we like its overall dimension.
We tend towards side sleeping which creates some difficulty in accessing the foot box. Because of my additional height, I usually control the position of the foot box, and if my date shifts fetal like, it's without the foot box. Unless we're on our backs, (like the picture on the Nunatak site), or spooned, equal access to the foot box is compromised. Nevertheless, we use it and find the ease of temperature management superior. We have used the quilt into the low twenties F.
If we were to order again, we would request a quantum shell with more fill in the top three channels because the down tends to migrate toward the ends of the channels, or sides of the quilt. We suspect because of our shoulder sleeping habits. We would also request a wider or larger girth dimension at the top of the foot box for a wider angle of access for feet/legs. This wouldn't completely solve the problem, but would help.
Although we often find ourselves in humid conditions, we sleep in a double wall tent and seldom experience interior condensation that threatens the quilt loft. I mention this because I recall your interest in a double bivy. Moisture transfer may be more important with your set up.
Good luck!