Hey - a general DS is about 1pg, double spaced. For people with really extraordinary circumstances, they are longer, but if that's not you, then 1 pg should be sufficient.
Ideally, you would cover different ground in your PS and your DS. Remember that you're crafting a package in an application - every part of the application should reveal a different aspect of you or your story. You can reiterate some of the things from your PS, but IMO, that would be kind of a waste of an additional statement.