Since you have to Rush through the Smokies to make it to SFOG, I say use the free day to explore the smokies national park.
A beautiful place. Also Gatlinburg has some cool stuff as well, Basically its like International drive in O-town, minus the high rises but you get my point.
If you like Go-karts the the best place ever is the Nascar Speed park.
Also for a nice relaxing dinner, Try the Peddler in Gatlinburg. Best steaks around, and its the only thing in Gatlinburg thats not Tacky.