I am an outspoken advocate of heavy arrows for heavy game, and pretty much everything else Ed Ashby has proven re arrow penetration and lethality. Out of more elk taken with bows than dignity allows me to count, the two cleanest and fastest kills both were shooting 13.7 per (two-blade heads, slender shafts, etc.) But I'm also confident that 10 per is plenty for deer, and I don't trust my accuracy with real heavy arrows beyond 13 yards, which is pretty limiting. I would drop to 10 for trophy bucks or even 9 for young bucks, does or pronghorn, to increase range.
Bottom line to me is that while we may miss some shot ops with heavy arrows, and sling a few low, that beats hell out of watching a gorgeous animal run off with an arrow flopping from it due to lousy penetration resulting from lack of momentum. The heavier the game, the heavier the arrow, that's my formula for no more heartbreak. dave