RE: Is 1 inch DIAMETER enough?
They have listed some of their clients on the website with kills on Moose and Caribou(with the Sonic 125) and I think Rocket has pictures of Hippo's and Rhino's taken with there Ultimate Steel.
One thing you have to remember is that with a larger diameter head 1 blade is surely to contact ribs on the way in thus dulling it to the point where it would not cut an artery.
Like I said before the Wasp Hammer SST I used 2 years ago on a large bull had 1 blade rolled and another dulled quite bad. At best I had 1 good blade, 1 that was so-so and 1 that was almost useless.
Like Rangerstud said, "shot palcement is the key" if you do not hit him right it doesn't matter if you broadhead is 1" or 1 3/16".