From eastern Iowa, you don't really have to go within 200 miles of Atlanta. Go through Memphis on down to the Gulf Coast (New Orleans, Biloxi or Mobile) then across I-10 to Florida.
I like going down through Jackson, Mississippi, then US-49 (to Biloxi) or US-49 and US-98 (to Mobile), but I-22 to Tupelo, US-45 and 45 Alt will also work. Or I-22 to Birmingham, I-65 to Montgomery, then US-231 down to I-10. I prefer US-49 because it is four-lane divided most of the way and has relatively few slow sections around the few cities that it connects.