Is there a substantial advantage to nasal breathing and not mouth breathing during moderate/high intensity exercise? or its better but not huge?

Good question.: The only real advantage to nasal breathing is warming cold air and filtering certain particles before they get into throat and lungs. At a certain point, the volume of air needed during exercise is more than can be delivered by nasal breathing alone. More important to keep up with oxygen demands as opposed to whether it is nose or mouth.

Breathing: While there have been some studies comparing nasal and oral breathing during exercise, most have used small sample sizes with somewhat inconclusive results. As such, breathing in a way that ensures your body is getting plenty of oxygen should be your goal - don't worry too much about the route.

Lots: Of articles on this. I believe that mouth breathing is more natural and less stressful during exercise. All the tests that have been done show no benefits with nose versus mouth breathing. May be a little help with dry regions due to humidity. But I say do what's comfortable.

Nose breathing: Nose breathing has advantage over mouth breathing because of the depth of breathing, the way the air is prepared and moisturized and get sterilized, when breathe with mouth usually is more shallow and faster and therefore the blood oxygenation is not as optimized. Therefore it is very important to breathe with nose, deep and slow to increase oxygenation during the exercise. Hope I have answered

No: Most air in yields more oxygen to body. Mouth much bigger than nose, therefore breath through your mouth. Take a few breaths each way and see what you think. Good Luck.