Hmm.. Maybe I have it reversed? The stories vary as to which one is the bigger one, so maybe the story I got is wrong..
My dad got the big one- he's much bigger than the other Jacks. My dad's is 25lbs (skinny). But the ratting drive is unbelievable. He won't stop till he gets them. He killed a squirrel in the blink of an eye, before my dad even knew there was a squirrel around.
My dad's Jack: