Old thread, but yes: the direction on the GAP was irrelevant to me when I did an up and back from/to Cumberland last year. What was a factor was the wind. Had a strong headwind the first day to Rockwood. That open section after crossing the divide was particularly bad.

Shameless plug for the GAP Trail Campground in W. Newton. Very nice facility close to the trail. Got to love the Hobbit showers.