A perspective from someone who's BTDT with a 165lb dog.
I won't name the breed, but it wasn't the one originally mentioned in the thread anyways, but I was attacked without warning by a very large dog that was 165lbs and could stand on it's hind legs and be taller than me at 6ft. It was my mother's dog and I was walking out her back door, when it came out of the hedges and lunged at my face. I instinctively put my left arm up which got the full on bite and shake treatment. We went for a nice roll across the ground where I ended up on top (think UFC mounted) and punching. I nearly knocked the dog unconscious (aim for just behind the ear BTW, disorients them like it does people to be punched there) and he went semi-limp.
Luckily when I put my left arm up I drove it far enough back into the dog's mouth that only one fang penetrated my forearm. This wasn't by design, but by complete luck and accident, but if ever attacked again I'll try to remember it as a purposeful tactic. This dog's head was almost horse sized, so he didn't drink out of the toilet, wouldn't fit, he stuck his head in the sink and barked when he was thirsty, but I digress. So, that size of head actually saved me from some severe muscle damage that day, by allowing my arm to fit mostly behind the fangs.
Had the dog not gone limp and stopped shaking my next resort was the folding knife clipped in my pocket. And once again it would have been just behind the ear looking for the brainstem or "off switch". I was too young to own a handgun at the time, but had one been available it would have been an option too.
The points I'm trying to make by this story are these:
1) When you're on the ground rolling with a large breed aggressive dog you are in a mortal fight, no different then when faced with a BG armed with a knife or gun. You can and may be killed if you don't react properly up to and including deadly force against the dog, he's using it against you after all. Had I not got my left arm into that dog's mouth it would have been my face/neck and I would likely have been severely injured if not killed and not sitting here typing this.
2) If I'm attacked by any dog, your dog, my dog, my mother's dog, my best friend's cousin (twice removed) -in-law on his aunt's side's dog, or just some stranger's dog on the street, I will react properly to the attack (see above).
3) It may not be the dog's fault that they have attacked you, I tend to agree with those dog owners who like to blame bad owners and say there are no bad dogs. Though I will disagree and say there are bad dogs created by bad owners. My mother was such an owner. That doesn't negate the situation that you may find yourself in when the dog is attacking you and the owner isn't around. It's not like you can walk around with the dog biting your throat looking for the owner to call the dog off or to defend yourself against. Your mortal threat at that moment in time is the dog and it is you or him.
4) As we've all seen typed in threads on SD from people, worrying about what's gonna happen in court later can get you killed when you are in "that moment". If I'm faced with a mortal threat from person or animal I'll defend myself with appropriate force and deal with the potential legal consequences later.
OK the above is my personal .02 and is worth exactly what you paid for it. I'm not a lawyer, I don't even play one on TV or the internet. I'm just a guy who's been severely bitten before who doesn't plan a repeat if possible.