We have some of the shoulder from our OSBs done as sausages to increase the amount, and generally get about 10lb per pig at weights similar to yours, that's sausages which are minimum 75% meat. I find that I can sell all the sausages and bacon that we produce (and then some), while roasting joints sell less well, so I have had almost all of a carcass sausaged before: seems a waste but that's what sells. When I take orders for 1/2 and 1/4 pigs, I ask the customer how they want it butchered (and if they want the heads, trotters & offal - most don't!) and tend to get most off the loin done as bacon cos that's what people want. Tend to get about 15lb bacon per pig too, give or take. Suggest you go and have a look at the carcasses at the butchers, and ask his advice about quantities. Make sure you specify high proportion of meat in the sausages too.