You might consider a 40-degree bag like the Western Mountaineering Mitylite. It might be multi-purpose enough that you won't need that second bag. I believe, from my own experience, that it may really be a 35-degree bag.

I camp in the same temperature ranges you do, in Ohio and Kentucky.

The Mitylite is a hoodless bag, and actually has 2 zippers: one around the foot, and a long one from ankle to shoulder. Unzip them both, and the bag lays open like a quilt at home. Zip only the foot zipper, and you have a quilt with a footbox. Zip up the long zipper, and leave the foot open for ventilation. Zip them both as the temperature falls.

In the warmer temperatures, I sleep in shorts and a T-shirt. Depending on how warm it is, I may leave the foot zipper closed. However, I always leave the side zipper open and use it like a quilt.

As the temperatures fall toward 40, I wear midweight long johns and top to sleep in, zip both zippers, and cinch the bag around my shoulders. I wear a stocking cap or balaclava, depending on temperature, to keep my head warm (no hood, remember?)

To go lower than 40, I take along down booties, light down jacket and pants (think Patagonia hooded down sweater and Montbell UL down inner pants), and maybe down mittens. You could use similar synthetic garments (Patagonia Micropuff hooded jacket and pants, for example.) This gives me clothing to sit around camp in the evening. I then simply wear some or all of it to bed, over midweight long johns and top. The hood on the jacket works as well as any sleeping bag hood (and lets you roll from side to side more easily.) I've used this combination of clothing and bag into the mid-20's and stayed nice and warm.

Lately, I've also been experimenting with a Thermarest Ventra quilt, though I haven't had it down to freezing yet. I like it, and took it down close to 40 with lightweight long johns and a stocking cap a couple of weeks ago. So far, I like it really well.

One last thing: if you're going to push a bag into colder weather, you might want to beef up that pad. It has an R2.2 rating; the Prolite Plus pads have an R3.8 rating. It won't matter how warm the bag is, if the cold seeps up from the ground. (But you probably already know that, and add padding in colder weather.)