The EIN 1357 ratings are good for comparing bags tested under the same system. One thing to beware of is how companies use the ratings. I've seen bags advertised at a temp that really is the survival rating once you see the full specs.

I have an old down bag, but I know the rating on it (not EIN 1357 as far as I know) is accurate for me because I have used it at the rated temp and below.

Sleeping on a pad or in winter, two pads, plus wearing a base layer and maybe even socks and a hat will help a lot if you are close to the rating temp. I wear a base layer anyway in winter and prefer to sleep in it.