I feel like the 300m Tuna and the Monster wear almost the same. In my opinion the monster wears slightly bigger due to the larger lug length.
I was expecting the Tuna to be a bit larger (about 2mm larger or so) but because of my small wrists, turned out to be fine. My limit to watches is around 45mm or so, so I was reluctant to buy the 1000m Tuna.
I'm guessing the 1000m (quartz or auto) Tuna's would fit you more if you are looking for a bigger watch than the Monster.
Here is some reference pics:
Seiko Tuna - please educate me