Got my sample today. For reference, I have a 37" waist, and about 238 lbs. I'm also 6'6." The current L/XL size "fits" snug, if I stretch them out a lot before hand but they tend to rub. They also don't cover my butt fully given how tall I am.
The XL go on easily without stretching. Yes, they're probably more stretched on the sides than they are for people who weigh less, but they aren't tearing, and aren't uncomfortable. They definitely appear to be and feel more padded in the front (which would make sense to me since I'd think an older kid would pee more). I don't know if the girls size has more padding in the middle or not. Definitely taller in the back, they almost completely cover my butt. I've had this one on (dry) for a couple hours now, and it's very comfortable.
I could totally wear these all day. Very excited for them to show up in stores.