Test 4: Basically the entire bathroom
I read in the aforementioned This Old House article that mirrors won't fog if you wax them. Let me set the record straight right now: that's completely and utterly false. Look at the photo above. The left side (horribly fogged) was waxed with the same carnauba I used on the chair. The right side (just as horribly fogged, but cleaner) features the sealant I used on the counter. That stripe in the middle with much, much less steam? That's the section I didn't touch.
It wasn't a complete waste, though. While you don't want your bathtub or shower floor to be slick, wax actually has the opposite effect when wet. If you wax your bathtub, you'll have much more grip than before because the water really doesn't want to stick to the surface. I tested it in a spot and confirmed: much less slick! It was, however, slick when dry, which isn't great. For tubs, there's actually a special type of wax made for wood floors that has -- stipulated by law -- friction modifiers so you don't slip and kill yourself. I'd recommend picking some up.