The only way to really tell is to actually try the various offerings out there and those recommended by others is a good starting point. But two guns of the same make and model can like shoot their best with different slugs.

I am not a big fan of the high speed slugs. Three of my favorites for big knockdown power would be the Remington BuckHammers, Brenneke 3-inch Gold Magnums and Brenneke 2-3/4-inch Heavy Field Magnums. I think the first two are 1-3/8 ounce lead and the 2-3/4-inch is 1-1/4 ounce.