There are clematis that will grow to 15' or more. From what I read, in GA you will do best with the type 3 prune summer-blooming varieties rather than the early large-flowered types. You will also want to avoid sweet autumn clematis since it seeds around invasively in your area, both in gardens and in wilder areas.

Sorry - I read too quickly and missed the fragrance requirement. There are a few large clematis that are scented, including Betty Corning and Clematis montana. I don't know how well C. montana grows in GA. You could ask on the Clematis forum or whatever is the most active forum for the SE.

You could also plant other scented plants in pots in the deck and that would give you more flexibility with your vines for shade.

Moonflower vine. I have grown these in pots. They flower quickly from seed and you can replant them every year. They come in white and lavender. The white ones are very fragrant in the evenings and early morning. I always find little tree frogs in the blossoms. They like to sit in the flowers and eat little gnats and moths that visit them due to the fragrance.