no matter how well you adapt to digesting fat, you will simply never ever be able to burn fat faster than carbs. there is no comparison to the amount of energy you can get from carbs to the amoutn of energy you can get from fat on a time measured basis.. hte more intense your exercise is the easier it will be to generate more energy if you are eating more carbs rather than more fat.
athletes in endurance races eventually hit the wall if they dont take enough sugar or carbs. they can burn their own body fat for a source of fat.. hte more you restrict carbs and sugar intake the more likely you are to experience a drop in energy output... thats why marathoners hit the wall. they run out of glucose because the intensity at which they exercise means they must get a certain percentage of their energy from glucose to offset the slower metabolism of energy from protein and fat.... find me an athlete who is running under 2 hours ten mins for a marathon that eats a high fat low carb diet,,,, I don't think they exist.... i used to be a harrier and i never came across anyone running under three hours or even three and a half hours who ate a low carb high fat diet....
people who undertake a lot of endurance exercise tend to already be capable of getting a fair bit of their energy out of fat. the body tries to spare its use of sugar as much as it can when burning large amounts of energy over a prolonged period of time and will burn as much fat as it can.. someone who is seasoned in endurance exercise will be able to get more energy from fat than someone who doesnt do much endurance exercise... thats been shown in studies on endurance athletes.. specifically ironman triathletes
from the land of the long white clouds...