You have quite a bit of info at your fingertips already .... but probably don't really know it.
What is your Rayway quilt made of? Polarguard 3D or Climashield?
Once you know what material you have already used then all you need to know is what the current CLO of what you have is. Then you can relate your personal experience with your 30 degree quilt to your current clo rating instead of loft.
If you're using a 3D quilt, like I was, then you'll find that that material had a CLO of around .63 and a weight of something like 2.7 ounces per square yard for the standard 30 degree quilt. This quilt was good to 40 degrees for me, so the temp was right on.
Two layers at 2.7 oz per layer, or 5.4 ounce, times .63, yields a clo of about 3.4. Therefore, for me, a 40 degrees was a clo of about 3.4.
I extrapolated from there.
One other note on temperature ratings ..... what are the other conditions outside?
Are you in a tent? Are you in the wind? Is there really high humidity? Do you have a good enough pad under you?
Do you have a good groundcloth?
All these factors, and more, can have an effect on temp rating. A mistake that many people make, myself included, is to expect a 30 degree bag, or quilt, to always keep you warm at 30 degrees.
If you're not well hydrated, well fed, too little insulation, sleeping under the stars in heavy dew, in the wind, etc .... you're not going to be warm at 30 degrees.