The 180 is my regular 3-season mountain quilt, combined with usually, the hoody and pants. I'm pretty comfortable in this system down to freezing or so. I know someone else who's fine in it down to 20, and another (a woman) who's cold in it at 40.
I've been chilly under a tarp (no bivy) with winds in this setup at 40 degrees, and comfortable at 25 in a tent with zero wind. Shelter from wind makes a big difference for any sleep system, I suppose.
What I really like for that 10-25 degree range, as I find in the fall here in Montana, is the 180, or a light down quilt, with the Pro 90 quilt as an overbag, with the hoody and pants. That is absolutely luxurious at 15 degrees but would be an inferno for me at freezing.