I don't think the number of plants matters as much as genetics, amount of useable light, and how they are grown. If you grow a big sativa, one plant can produce 2 pounds all by itself. Of course, I'm talking the 10' tall or bigger ones. The commonly thought of 'holy grail' is 1 gram per watt, which most newer growers do not reach, but experienced growers can exceed. If you go by that, then 1000 watts should get you 2.2 pounds. Personally, I aim for half a gram per watt, and then if it goes beyond that, I'm very happy. If I were you, I'd be happy with a pound, and count everything beyond that as bonus bud.