The poster used the example of a bus vs a sportscar to illustrate the point he was trying to make - in that momentum is much more important to consider when it comes to killing a deer. Sometimes you have to use an example like that for a person to truly understand what you are talking about when you say something like "momentum". (the train wreck being a good one too) Because once the arrow starts to enter the deer, you have things like ribs, cartilage, sinews, etc to smash through on the way to becoming a pass through shot. When I first started hunting, I used 85gr broadhead arrows. Wow all I needed was one pin to aim dead on out to 35 yds!! Now I use 125 grain broadheads, with heavier aluminum arrows to hunt with, and I get better damage. I also do not have a flat shooting arrow, with my bow cranked down to 53 pounds! I have to know my shot distance. Not sure what the equivalent weight comparison is, but how about getting hit with a sports car vs a pickup truck? You get the idea. I'm not saying kinetic energy means nothing - not at all. But sometimes I think the bow manufacturers use kinetic energy numbers just to sell more bows. If I were target/competition shooting, there is no doubt in my mind that I would use the flatest shooting rig I could.

So it is all a trade off. Heavier, "rainbow" shooting arrows vs light flat shooting arrows.