It's the old 'everyone's different' story PP
I tend to find with my crossbred weaners, (cos I've not done pure bred weaners for eating yet) that by 6 months they're looking ready to go for pork. I aim for about 85Kg liveweight to give a carcass weight of 50Kg and 35-40Kg of pork. Nothing as scientific as weighing or measuring anymore - I just go by eye, when the back legs look like a ham they're ready for the off
For baconers they tend to be older and heavier, 8-10 months but I'm not sure on the killing out weights on that. I just got a 6 month pig cured and the bacon, although a bit smaller was every bit as good. I think the theory is that as they get a bit older the meat gets a bit tougher, which is why traditionally pork pigs go @ 6 months to keep the joints nice and tender.
So it's a case of what weight and size are your abbatoir able to take, do your customers want cured or uncured pork and you do the costings to reflect the extra time, feeding etc.
HTH
Karen x