Dose for peroxide is based on size, and you can redose if needed. Age, health, and size all play a role in survival. Milk chocolate is unlikely to kill, dark chocolate definately can. 
I lost my 15 year old schipperke to a few ounces dark chocolate last June. It looked like the german shepherd had pulled the bag off the counter, but not eaten any. The schipperke was smart on opening bags. I caught her in the act, called the vet and induced vomiting. Then got her to the vet immediately. They induced vomiting again and got more out, then charcoaled her. About half an hour later the seizures started. They tried giving her stuff to stop the seizures but it didn't help. She just was to old and her body wasn't up to par to win the fight. 
I still miss her a great deal. She was my best friend through a divorce, remarriage, and my husbands military deployments. All chocolate of any sort is kept up very high now. I've also warned my brother on the chocolate. He got two toy dogs this past summer which are much tinier than a schipperke. He was told by a friend of his that the chocolate toxicity was a myth and believed them.