Its like a good blade. You want hard enough to hold a edge but not so brittle as to break or chip under pressure.Along w. the Janka hardness, I've found the modulus of elasticity to be valuable. The hardness is a good indicator of how hard (or not) carving will be. But the elasticity seems to be a good indicator of durability. Hickory isn't the hardest, but over all seems the best for rugged use as it is more flexible than harder woods.