I've only ridden at Road Atlanta once, but I still have stock gearing; 16/42. I was NOT topping the bike out on the back straight and as long as I was doing my part, the bike had plenty of get up and go. The biggest areas of concern I saw were in the exit of T5. I think one morning session found me 1 or 2 gears too high and the bike was a dog coming up and out.
Was bumped into I group after lunch and ran the last 2 sessions there. Even still, I wasnt quite at the top end of the bike. I THINK I saw 153 on the speedo coming down the hill, still braking way early into T10.
I think T1 would be a crucial area as well to be in the right gear as you work back up the hill, but I struggled in T1 all day.