I think if you're planning on having an Old-blood on a Carnosaur, it's worth the extra points to take Kroq-Gar. He hits harder, he forces leadership tests like a mad-man, and if he dies, you don't have to worry about the Carnosaur suddenly becoming unbreakable.... and immobile. I like the idea of Lord Kroak, but I just don't think he's worth that many points.