Considering the summer temperatures in Atlanta, I would go to synthetic just for it's stability at high temperatures. My synthetic oil experiences:

1. A two year-old 1991 Dodge Monaco with a 3 liter V-6 (essentially a Volvo 164 engine) and 20,000 miles = oil leaks

2. Currently, a 1999 Ford Expedition with 41,000 miles = dry as a bone

Both vehicles ran on conventional oil for 20K before a switchover to Mobil 1. Used manufacturer recommended viscosity.