I use a different goggle for swimming (the seal of the X-Sight on my face isn't good enough for swimming), but the X-Sight seals well against the headwind of biking, and it provides good peripheral vision that is very rare in a swim goggle. I've worn them on rides as long as nine hours. As an extra bonus, these are ideal eyewear for riding in the rain, and they will also keep the bugs out of your eyes on slow backwoods mountain bike climbs.
The goggles have an antifog coating, but lke any other fully sealed goggle, they will fog up in use. In the swimming pool, you'd solve this by admitting some water to the goggle and sloshing it around. What I do instead is to squirt in some saline solution (Sodium Chloride Inhalation Solution USP, 0.9%, 5ml, made by Dey and sold by MediChest.com) into the bottom of the goggles while I wear them. When they fog up, I slosh this around and it defogs the goggle. One application of slosh-water was enough for my 9-hour bike ride, though I do carry extra vials of the saline solution on my bike in case for some reason I need to remove the goggles and then put them back on again.
I have found with these goggles that the antifog coating is very durable. For effectiveness, it requires cleaning prior to each use, using a dilute solution of Dawn dishwashing detergent and water, followed by a thorough rinse with warm water.
In general, for biking and boating it is not difficult to keep the slosh-water out of my eyes. I think this is advisable for hygiene reasons. For some other applications that involve inversions (e.g. gymnastics, dancing, yoga), the slosh-water might become problematic.
The use of slosh-water can be problematic at temperatures below freezing. I have never seen it cold enough to freeze the saline solution, but the cold liquid against the face may shorten your comfortable outdoor activity time.