Like BGfisher says, always err on the stiff side. It's easier to correct problems. Also, arrow length plays an important part in this, and the arrow charts do not take it into consideration. If you like a bit longer shaft to keep broadheads clear of your hand, then you need a stiffer arrow than the charts recommend. Add in the fact that most carbon arrows tend to be rated slightly stiffer than they actuall shoot. Add all this together and one can see why stiffer is better - much better.