Jonathan,

I think the max added weight in that table is the most weight you will need to add if you are underweight according to your class rules...i.e. if the max added weight is 65lbs, you're minimum class weight is specified at 325lb (the weight of both crew), and you're actual combined weight is 250lbs, the most weight you would need to add to meet the rules is 65lbs (in this case it would only get you to 315lbs). I don't image that max weight is used very often.

What kind of boat do you have? I'm sure we could give you a good idea of what to expect with a certain number of people on board.