I ran clockwise, starting on the east trails and finishing on the west trails. I couldn't find a total elevation gain online but my Strava activity said the route was about 2,200 ft.
Total time was 2h, 44m, 04s (Strava time was the moving time and slightly less), I did it Unsupported.
I ran the Park Loop/Green Route in the Northern, Central, and Southern section maps posted on the National Park Service website, Rev. 1.10 created by Larry Knight (thanks Larry!).
https://www.nps.gov/kemo/planyourvisit/maps.htm
The only real choice is when to cut over from Camp Brumby Trail to Noses Creek Trail and the Park Loop does on the Pigeon Hill Cutoff.
There were a few downed trees on the east section but otherwise the trail was in good shape. One very small creek crossing.
There was not too much traffic at the Burnt Hickory Rd crossing. There was significantly more at the Dallas Hwy/Whitlock Ave crossing but pushing the button at the pedestrian crossing stopped the cars quickly with a light.
I took one wrong turn just after crossing Cheatham Hill Rd on the west section, I didn't see the trail marker and turned right onto Kolb Farm Connector instead of left onto Kolb Farm West Connector. I realized after a few tenths of a mile and turned around, which added a little bit to the total mileage.
There were a couple non-obvious sections:
-The top of Pigeon Hill did not seem to have a defined trail but had many paths through the boulders
-There's a sharp left turn coming down Kennesaw Mountain that is easy to miss
Great weather, awesome run!