Chad, to get an arrow to penetrate you need inertia. An object gets its inertia from its mass, making speed somewhat irrelavent. Obviously you don' t want a dog of an arrow that has to flag a snail down, but regardless of how fast the arrow is, if it' s easy to get it in motion it' s also easy to get it out of motion. That' s not something that sounds good when talking about big Aussie Water Buffalo. 85@30 with 31" bop and 160gr broadheads you' ll obviously have enough weight and thump to handle a lot of animal. If you' re using a large broadhead it should cut flesh and such to make way for the shaft. You could try to contact some Aussie guides and people who' ve bowhunted Waterbuffalo and see what they say about it. I reckon they' d know more about it anyways.

Brandan