If I was starting from scratch, and I wanted a 3 season system that could handle lows down to 20 but also temps up into the 50-60s on warm summer nights, my personal preference would be a quilt that handles 30 35 degree temps, so I wouldn't be too warm in the higher temps, but warm enough to be boosted into the 20s by the addition of a hooded parka. The ones you mentioned or a Montbell Inner Down for 25 degrees or an Alpine Down for colder.
In other words, the Nunatak Arc at 32* would be my ideal bag + a skaha. Throw in a MLD or TiGoat bivy for wet conditions, or to boost the warmth a couple more degrees, and you're set. (I already own the MB jackets, but if I was starting from scratch. . . ) But that's a pricey system.
A more economical, but still quality system could be a Jacks R Better No Sniveler, which is a bit warmer than I'd want at 25-30 degree, (but it's a quilt, so easy venting) + the MB jackets I mentioned.
The thing about the JRB quilt is that with the head hole, you can buy the down hood and down sleeves separately, and for cool but not cold conditions have an all in one quilt + jacket system.
Right now I have a WM Summerlite + the MB jackets + Tigoat bivy for the conditions you mentioned. The Summerlite is a full zip bag so easily quilted. I'v only used it in the mid-40s (I had to unzip and quilt it) and mid-30s so far, so can't fully review it's capabilities.