I would have no trouble identifing one from the other by sitting on em blindfolded. The width and added springiness of the b17 are a dead giveaway, as well as the presence of those little ridges up the sides. This isnt indicative of any super butt sensitivity on my part either, they're just way different.

Wow now that's a worn out b17! Give tying a try though, it does make quite a difference. You can reef on the laces and add quite a lot of tension that way.