Greetings & welcome,

I can't give direct advice about those sleeping bag choices, but I can share what I've learned from lightweight backpacking reguarding sleeping bags. A lot of lightweight hikers use a "sleep system" as opposed to just a bag: they use an insulative jacket, long underwear, warm hat, or other clothing along with a sleeping bag so that they can get away with a lighter bag. My impression is that 30-40 degree bags are pretty typical for lightweight hikers in the lower 48, with down being the prefered material.

Depending on the typical overnight lows, windchill, and wetness of your area, I think you'd be fine with the +20 degree bag vs the 0 degree one. I usually use a 32 degree bag, though for years I used a summer weight quilt that kept me warmish down to about freezing when I wore most of my clothes. I do most of my hiking in NW Washington and SE Alaska.

The choice of sleeping pad can also have an effect on warmth; inflatables allow air to transfer heat from the body to the ground more than foam pads. Some people carry an extra, really thin foam pad when it gets cold out. Some people also sleep on their empty backpacks, usually under their legs when they use a short sleeping pad.