There really are a lot of great models to choose from!
Think about what you'll use a larger knife for. The 7/7 is longer and a little heavier that the 5.1, so you can span a little bigger wood for batoning, but I don't think either would chop amazingly well. The 8 is specifically designed for larger work. It has a taller (edge to spine) blade and might even be thicker than the other 2 knives mentioned, but I'd have to check. The 8 will be heavier and better for chopping, bit not too big.
BUT if you're already planning on an axe for chopping it might not make a difference for your uses.
All that said, I'd still be really interested to hear from someone who has handled some of these models before.