If you've read the Ashby reports you'll quickly discover the advantage of heavier and higher FOC arrows. The added mass provides more momentum which enables the arrow to keep moving forward even after it's encountered the game animal. This can be especially helpful if/when bone is in the path as the increased weight helps the arrow and broadhead to go deeper to get to the vitals and increases the potential for a lethal hit.
As far as accuracy goes, I've experienced an improvement in tighter groups with higher weight and FOC arrows. They also aren't affected by winds, especially cross winds, as much as lighter weight/FOC arrows.
2008 Martin Firecat Pro-X (29" DL, 66# DW), home-made TRG, new VEMs, DS Advantage/HHA Pro-5519 front sight, No-Peep Sight Eliminator, Limb-Driver arrow rest, B-Stinger stabilizer/dampener, custom upper STS, G5 Head-Loc quiver on custom mounting bracket. Gold Tip Velocity XT300 arrows with Bi-Delta 2.5" Sharkstooth vanes and Grizzly single-bevel broadheads, 498 grains at 262 fps (22% FOC)