I think that crosses end up being less muscular and just larger (depending, of course, on the breed it is crossed with). Boers usually give out the most meat. Dressing percentage for goats is 40% to 60% (don't quote me on that...), so it depends on your wether's weight and condition.
Since Boers are bred for meat I would expect that you'd get more as opposed to a dairy cross. I think you can get around 50% after processing from liveweight from meat goats.. They also are bred to put muscle on quickly with less grain, whereas dairy is opposite, everything is supposed to go into making milk, so they are a littler slower growing. I've never raised for meat though, so I'm probably not very helpful..
I have only raised 1 goat for meat. That was a Numancha wether last year. He stayed on his mother until a month before he was shipped, which was 6 or seven months. I got 2 large boxes of packaged meat from him, I forgot how many pounds of meat, but when I posted it on another site, they didn't believe I got so much. I don't know, I saw it weighed so i know how much meat was in those boxes.
I have a friend who has Boers and Boer/dairy crosses. She swears that the Boer/Nubian crosses produce more meat earlier than the Boer alone. She said she gets the Boer muscle on a faster growing dairy frame. I don't know if this is true or not, but this is how she makes her living, so I don't doubt her. I never butchered any of the Boers I used to have, I sold them all to her.