Dark Impale Question

That hasn't been true since Big Bang. Dragon Buster was only good for spears because it forced a stabbing animation and spears did more damage stabbing, while Dragon Fury was better for pole arms because it forced a swinging animation and pole arms did more damage swinging. Since Big Bang, there's no damage difference between stabbing and swinging with either weapon anymore. You can freely use either without fear of doing less damage, though pole arms are generally faster than spears, and spears have more attack, I can't really say if the extra attack on spears is enough to make up for the slower weapon speed.