I've never butchered a home raised chicken, although I have had and given away many. Supposedly ducks are all dark meat because they get a chance to fly and use their wing muscles.
My birds fly
My birds are very flighty.I hop for dark meat as well.
I'm throwing a dart at the board here. But I'd bet a 6lb bird is going to clean out around 4 lbs.
Let me go kill one of my chickens, I'll get back to you.