A few months ago I bought 4 EB blankets from Costco to make 3 underquilts and one top quilt. Last week I got a chance to test their limits. I was in the Smoky Mountains with an overnight low near 34F. Since I read these are good to about 50, maybe 40, I planned on layering up with extra clothes. My primary goal the first night at base camp was test if I would freeze. Second night was about keeping my pack light.
The results are that I didn't freeze but I wouldn't call it cozy either, more like survivable. I was slightly chilly but managed several hours of sleep. So I think it was successful.
The third and fourth night I was back at base camp where I added a second underquilt and pulled out the 30 degree bag. That made those nights cozy.
So I'm actually impressed that I got usable performance that low on the thermometer.
I'll try to remember to post a photo later.