It's not just about total arrow weight. The biggest reason to go heavy is to redistribute more weight to the front of the arrow. Arrows with heavy front ends and lots of drag on the rear, fly straighter through wind and when hitting small twigs. I personally don't give a rat's rear end about any speed gains from a lighter head. Heavier heads fly better when conditions aren't all that good. Quite often when I hunt, there's a breeze or a pretty good chances of hitting a small twig, leaf or weed. I make sure my arrow shaft is stiff enough to handle a higher weight broadhead, which will increase my chance of success in many situations.