I75 or I77 from SE MI to St. Augustine, FL.

With the fire in Atlanta I-77 would be your best route. If you stick to the interstate you will get into traffic on I-95 after you get off of I-26 if you travel on the weekend. Most of the Snowbirds are leaving Florida now and headed home so there is a possibility that the trip South could be smooth. If you like running the back roads like I do, at Orangeburg, SC.{off I-26} pick up US-601 to US-301 to Jacksonville and on to 395 South to St. Augustine. Good road, no traffic just small towns and lots to see.

I drove down in December and ran into a little traffic in N Carolina as well, but it really slowed to a crawl north of the Hardeeville exit on I-95. I think it took me a couple hours to get through that mess.

I am not sure how the big fire on 885 will effect 875 but i am sure it will. I live South of Atlanta and use I75 but will now avoid Atlanta as much as possible.