I dont have much to add that hasnt already been said, but one thing about pivoting on the base leg vs not pivoting on it... I used to not turn the base leg (it would be 90 degrees from the target) which allowed a much faster kick. I could still get to about rib height this way. Recently an instructor told me while this may be faster, its not as powerful becasue the way your body is aligned. I always knew it was weaker but apparently thats becasue when you pivot your base foot 180 degrees, your frame lines up so the hip socket doesnt have as much tension on it. While it may be not as good for the knees, its better for your hips. Ahh, the tradeoffs...