Temp rating?
One for every thing from CO to AK hunting.
I have been through this very situation several times, due to space limits when working alone in remote wilderness, using my own gear and needing items that would double for hunting, camping (BC-12 months of the year) and even as bedding when in college.
I use both synthetic and down bags, do prefer a REALLY FINE down bag and have/do own most of the big names. At present, I would suggest either a Western Mountaineering Kodiak or a Valandre Shocking Blue and buy the WM in "microfiber", use a bivy if in really wet conditions.
That said, I actually have/do use two down bags for most things, a -20 model, mine is the fabulous ORIGINAL XPDII and it was custom made for me by Integral Designs of Calgary, AB. I have never seen/used a better bag in my 50+ years of use in northern and western Canada.
I sold my last light bag, an Alpinlight, by WM and will soon buy a WM Terralite to replace it, just due to more space. I like to have a 20-25*F down bag as well as the -20*F type and have done this for almost 40 years.....get the 0* to -20*F one if one is all you want or can afford and buy the BEST, it really pays off.