I'll say it again--talk to guys like Rick McGowan, Don Thomas, Billy Baker, Cory Mattson, Denny Sturgis Jr., Ed Ashby, etc. etc. etc. You might also do some reading in the Dangerous Game forum and Dr. Ashby's reports.
Ric has seen what light arrows shot from super fast compounds will do on thick-skinned, heavy boned critters, and he's seen what very heavy and relatively slow arrows will do. Guess which one he uses?
On most of the animals most of use will hunt, it's not going to be a big deal. When your butt's on the line with a critter that can and will hunt you back, you don't fool around. Look at the years and years of combined experience to get the facts on the big picture.
The reason this interests me so much is I've been planning a big game hunt for several years now. I've talked with several big game hunters and guides, read over different test reports done both on different mediums--live animals, dead animals, animal parts, etc. etc. etc.
If you want to test your luck and your standing with the Good Lord, go ahead and chase a buffalo with a 500 grain arrow. I'm just not the type to press my luck like that. When I go, I plan on having arrows that weigh in at no less than 800 grains, preferably closer to 1,000. Besides not being able to stomach screwing up after all the time and expense of a trip like that, I want to keep all my parts right were they are now!
Chad