I live in the Atlanta area, and I can tell you that going straight through is the best option, unless you like lots and lots of semi trucks. Those times are both outside of the normal rush hours and should be ok. There will still be a lot of traffic, but, it usually moves (fast). As was stated, stay in the middle lanes of the highway, the right lanes disappear. Either that or use the HOV lanes, at least until you get past the I-20 interchange. You may experience a little slow-down where I-75 and I-85 join, but, it's usually only for about 1/2 mile or so. I-285W has become very bumpy due to the truck traffic, and there are some sizeable pot holes in the middle of the road, especially in the right two lanes. Don't over think it and you'll be fine. I worked in downtown Atlanta for 30 years and only occasionally had issues (of course I live southwest of the city, down I-85, and that makes a huge difference).