I did a pattern comparison with a friend of mine a few months ago. The buffered Federal 00 was the best. For us, anyhow. If I remember, I was shooting 2 3/4s and getting an 8" pattern with the 9 pellet Federal @ 30 yards from a cylinder bore.
I wish you luck with your hunt and hope that you get a chance to come up north and hunt real whitetails. The kind you can't use shot on.
Stopping power: The power some guns have to make you stop what you are doing and get your wallet out.