Regardless of their actual dimensions, in my experience, goats are surprisingly stout. I've seen three mountain goats killed (one myself) and a pile of feral goats in New Zealand. Two situations stand out.
One was a broadside mature billy high on a ridge in British Columbia. My buddy shot him perfectly with a .280 AI, and he didn't even twitch. We all thought he'd missed. After another perfect shot, the billy walked off like nothing had happened and then fell dead over a snow cornice.
The next one was even more stunning. It was a feral goat my buddy wounded in the mountains of the South Island, New Zealand. I chased after him to finish the job and found the billy behind a rock outcropping, maybe 70 yards away, obviously hurt.
Being low on ammo at this point (because of all the goats), I carefully dumped three 120-grain pills into his lungs over a 60 second period. After each shot, I expected him to drop. Finally he did, but his heart/lungs must have been jelly. I get that he was wounded and therefore high on adrenaline, but man, that one was crazy.