I remember we discussed one ultra-marathoner who went low-carb and improved his performance. In fact, he won that race by a large margin. Dunno how much carbs he ate, but it was much lower carb than he used to eat. I remember he explained the biggest problem isn't really energy, it's the gut. Many of them get to a point where they can't eat or drink anymore, cuz they just puke it out. Another problem is at the other end, they literally had to go several times during a race. With low-carb, that guy didn't have any of those problems anymore. When the race is 12 hours, these things make a big difference.

Since this gut problem makes such a big difference, I'm not sure we can draw any conclusion about energy or anything else just based on this anecdote. But then again, even if that's all it takes to win a race, who cares what else it can do.