I agree that a 400-500 pound sow is some of the best eating. There are a lot of people that think that the only thing you can do with them is make lots of sausage, but I totally disagree. I haven't eaten one over three, but I don't think they will get much tougher. They will put on a lot of fat that you can either trim off and
compost or sell to people making lard (if you don't want to). This adds lots of flavor to the sows.
The main thing to realize is that all of the muscles get proportionally bigger. This can make selling whole or even half hams difficult. A 30-40 pound ham is expensive. The cut I really like and use most often myself is the chops. I have them cut at an inch to an inch and a half. This gives 1.5 to 2 pound chops that I sell as Pork Porterhouses. They are great on the grill because they have a nice bit of fat to flavor them and I cook them like I would a bone-in ribeye except I go to a medium to medium well on them instead of medium rare.
The reason commercial producers sell market hogs at 200-240 pounds is that at that point the feed conversion peaks and starts to quickly go down. We usually butcher ours at 300-350 pounds because we want more flavorful pork and also that is the point they start getting a good slab of pork belly for bacon.