Back in the day when I was doing performance distance running (and all of the training that goes with it), most of my early morning runs were done in a fasted state. Most of those weren't more than 1hr in length, but they were fairly brisk, often hard.
Invariably, though, with higher intensity I always found that eating appropriately about two hours prior to a hard effort would result in better performance. Same with longer periods of moderate (say, 2.5 to 3hr runs instead of 1hr runs).
Never did hit it as hard with cycling, myself, so I couldn't say. But I can't see how it'd be much different. At a given level of intensity, beyond a certain amount of time, generally speaking the body can use more fueling. Where that point is, with a given individual, will almost certainly vary from person to person.