Answer: As you yourself have pointed out, it's so often six of one and half a dozen of the other, which of course is what makes gardening so interesting and so much fun. To be honest the only way to know about specific borderline plants is to experiment and see what happens, knowing of course that the results may differ from year to year. I am not surprised that the HA (hardy annual) types will overwinter for you. The HHA types, however, as a rule are not frost tolerant and should not in a climate with freezing temperatures.
The Moon Flower Vine is a twiner with a large leaf and large flowers, and although it is of a relatively finite length (about 12 feet), it is a large plant. It begins to grow once the soil warms in the spring and grows quite quickly. Since this plant is a tender perennial rated to zone 10, I doubt it would survive even a mild winter in your zone 7b.
The daturas and their relatives the brugmansias are native to warm temperature regions and are grown as conservatory plants if they are to be overwintered in their full glory. If the prospect of bringing a rather large shrubby plant into the house is a daunting one, you might consider rooting cuttings to overwinter them in that form instead. The size transformation from cutting to full blooming size is dramatic, so many gardeners prefer to keep them in containers so they can be uppotted as needed and rearranged as they grow.
Enjoy your plants!
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