RE: Larger diameter advantage?
You bring up an interesting topic for discussion. I have often thought that all that really matters in the world of terminal ballistics is the size and shape of the permanent wound channel. There does seem to be some validity to the claim that when a large bullet enters an animal, it allows air to come into the wound better (the better to collapsethe lungs) and blood to more effeciently leak out.
But generally speaking the main advantage to a big bore gun is that the bullet weight can be increased quite a bit. I'm just not sure that, in this day and age of high tech bullets, whether bullet weight is anywhere near as important as is was 30 years ago. I shot an elk in 2002 with a Barnes X bullet out of a .300 Winchester; and found the wound channel to be about the same as what I got from a .45-70 pushing a 405 grain Keith style lead bullet. Not that I'm advocating elephant hunting with a .300 Winchester, but it's fairly amazing how well some of these new bullets can penetrate.