Well, the argument threads tend to polarize, don't they G2. Of course, some guys think you're talking about hurling telephone poles when you say 400 grains.

Going extra heavy is just as bad an idea as going extra light, except you don't have to worry about tearing up your bow with extra heavy arrows.

The real answer is the same one that's been around since well before compounds. "For hunting, use the heaviest arrow that will still give you acceptable trajectory." What is acceptable trajectory? That's for the individual to decide.

Within 30 yards, trajectory doesn't vary hardly at all between an arrow at 5 grains per pound and one at 8 grains per pound. If one limits his shots to 30 yards, might as well use the heavier arrow. The extra weight carries more energy from the bow and carries it further downrange than the light one. More energy at the animal = better penetration.

Beyond 30 yards? If I ever decided it was worth taking a bow shot beyond 30 yards (might as well be using a rifle, IMO), I'd still use a moderate weight arrow and a rangefinder. Ultralight arrows give you a tad more leeway in yardage estimation, but not that much. A hunter should still know the exact distance to the animal. And, since the moderate weight arrow would start off with more energy at the bow, and carry a bigger percentate of that energy downrange than the ultralight one, it makes sense to me that it'd giveme better penetration and improvemy odds of making a quick, clean kill. If all doesn't go according to plan and I hit bone, the extra bit of energy can't hurt my chances of busting through it and into the vitals.

Super flat trajectory is nice to have, but I'dmuch prefer to increase my odds of making that quick, clean kill.