See my siggy
429 chopped an additional half hour off our trip (we also live north of atlanta), our last run down in April we made it door to door in 6 1/2 hours

. SO glad they put it in-there was NO traffic at all at 10 am on a weekday during the height of spring break, unlike I-4 which is such a night mare-just avoid it at all costs.
The locust grove exit south of atlanta can be a real bottleneck during the day, both coming and going.
We always go down 400 in Atlanta and take the downtown connector to 75, we never use the Perimeter (285), it's always slower.
We always leave at 3 am because there's *no* traffic and the kids sleep. We get into Disney around 10 am, check in, goof off at DTD or the pool, or if we get lucky check into our room, and still have the whole day in front of us. We usually nap in the afternoon anyway so the early wake up doesn't mess with us.
Avoid the BP gas stations, the bathrooms are gross.
There's a combination gas station/mcdonalds about halfway down (south of macon) that's good to stop at-clean bathrooms. We usually do one pit stop for food/gas/peeing and that's the one we stop at. You'd think I could remember the exit, but our daughters' bladders seem to magically know when to stop and it's always there.
Take the bypass in Macon, don't go through Macon. Um, 475, I think it's called.
Be careful once you get on the 429, there are a couple of speed traps. Our friends who drove down with us got caught, and we were going fast enough that the cop flashed his lights at us to slow down. There are some handy pockets on that hwy for the police to hide in so take it easy.
And if you see a gold mazda minivan covered in disney stickers with georgia plates, that's us! (we'll probably be doing 90 mph with our hair on fire!)
Oh yeah, which reminds me, if you're driving through Georgia but you're not from Georgia, be prepared for ridiculously fast speeds on the highway.
Much of 75 has a 70 mph speed limit, and that's what people do in the SLOW lane. If you're in the fast lane, be prepared to do 90+. I kid you not. We typically do between 80-90 mph, (we have Z rated speed tires!), and it is not unusual to be passed. Just get out of the fast lane.
And if you have tags from the northeast, especially NY or NJ, state troopers love to pull you over-it's one of the more amusing past times to see where the plates are from on the pulled over vehicles. In our experience it's the out of state plates that get bagged.