Ratings are pretty unreliable unless they list the EN rating. EN ratings should be consistent, but not necessarily correct for each individual.
You need to see what works for you. I must put out heat like a furnace because I have done fine with a bag rated for much warmer conditions than I use it for. I used a Mountain Hardwear Phantom 45 in a wider range of conditions than you list in your post. I have slept in it many nights below freezing and have even slept in it (in a bivy) with a layer of clothing and two pairs of socks at 18 F. I was just fine. On the other hand lots of folks are apparently cold in the same bag at 45 F.
Regardless of the bag choice that works for you, warmth can be tailored to the conditions. At the warm end of the range I sleep on the mat with no bag. As things cool down I use the zipped open bag as a quilt exposing a leg or my torso if necessary to stay cool enough. Next I climb into the bag. As it gets cooler yet, I zip the bag, then put on the hood, and then cinch the hood to a small opening to breath through. If necessary you can loosely lay extra clothing on top of you for additional warmth. You can also use a down jacket or sweater for extra warmth.