In reply to Langdon's post and his reply to my PM.
Light Sussex were, along with Rhode and Plymouth Rocks and a few others, used as a dual purpose breed in the past. They were reasonable layers and the cockerels were run on for the table, but mainly concidered as un-profitable,but a few things have change since those days I'm afraid.
Firstly everybody has got used to seeing Jordans (birds with big breasts) since the commercial poultry producers started using 'meat strains' these have taken over from the traditional farmbirds of old along with layers in the form of hybrids.
You will not get any more meat on a bird than that type/strain/breed is bred for and most of the best strains have been lost through bad breeding practices. Any traditional breed once it has filled it's potential the rest goes to subcutaneous fat and usually disposed of.
Unless crossed to a double mustled breed like an Indian Game you will not get a very good return on a feed for flesh ratio.
All the commercial meat breeds are a hybrid of more than 2 breeds.