Good question, and something I plan on following up on with my pet nutrition professor for more information. I do not recall ever discussing this subject in our class. Here are my thoughts however, based on my current knowledge. Cats are not really grazers, but we have made them into grazers with the high carbohydrate food we feed them. They are naturally carnivores and when living on their own survived by hunting rodents and other small animals such as lizards.
Dogs, descended from wolves, or at least very closely related to them, are omnivores. They may actually be more scavenger and grazer than felines, except that when wolves and other canines hunt they typically feed off the food immediately and cache some for later. They frequently drag some of their food away from the kill site to eat. They may eat leisurely, but typically wolves are pretty hungry by the time they have made a kill and dig right in. I think there are dogs that eat quickly and dogs that don't.
I had a German Shepherd who I had to work at getting to eat, and currently have a Golden Retriever who would eat until she couldn't eat anymore!
In my experience, breed as well as individual experience affect a dog's appetite. For example, dogs that have been nutritionally deprived - starved - tend to eat a lot, given the opportunity. Golden Retrievers and Labrador Retrievers love to eat and tend to gain weight.