I have had (from British Toggenburg males at 10 months) a deadweight of 24kgs (didn't record live weight), which turned into about 13kgs of meat (2 hindlegs on the bone at about 2 - 2.5kgs each), rest either cubed or minced). Probably not quite the same return as you would get on a lamb (texel or similar size) at that age, but really quite lean, and as I said needs concentrates and milk for longer than lamb would. Tastes however quite different to lamb - much nicer (but then I don't like lamb, prefer mutton).
I don't really know much about carcass sizes for Boers, but the bone/meat ratio should be better.