I am please to report that all went well on our drive both there and back. We stoppedin Louisville both on the way there and back (Visited Six Flags Kentucky Kingdom!), so we took I-65, did not have an major traffic snarls at all.
Left Sunday Morning at 3:45AM Chicago time, and arrived at midnight that night! We were actually planning to stay the night somwhere between Atlanta and Ocala (Valdosta, more than likely), but felt fine to drive all the way to WDW! I drove the entire way other than the last two hours.
On the way back we left WDW at about 4:30pm and stopped just shy of Chattanooga by about 30 minutes at about 1:00am. Got back on the road the following morning at about 9:30 am, and arrived home by 9:00pm that night. This time my wife drove the last 5 hours or so.
I was so comfortable with the drive I almost feel like, why ever fly to WDW again?