Sick dude! for impact frames, use the background. on contact, move the background upward and then for the next frame bring it back to it's original spot. The quicker the contact frame the better(for the most part). I like what you did for black's punch, that screamed impact.
Experimental idea: (if you use a background) the lines you used to represent rushing wind or emphasize speed, try lowering the opacity. It should make for a cleaner presentation