I have 1000w in a 4x4 with 5 plants and yeild 15+ ounces. Like the others said though, it depends on alot of things. I would say no less than 5 with 2+ plants assuming you know what you are doing and do everything correctly.
It's going to depend on what strain you're growing and how good the grower is that's doing it. The key to getting more off a plant is making sure that each plant's trip through life is as joyous as it can possibly be. Every stressor is going to have a negative affect on a plant, regardless of how big or small the stressor is. If you can keep the plant healthy and pumping from start to finish and grow a strain that is a known big producer, you should easily pull a pound from 4 or 5 plants with that setup. I run 4 1000 watt hps lights in our flower room and generally flower off 15 to 20 plants each run with a yield of 4 to 5 pounds depending on what strain I'm flowering at the time. Keep those roots happy and the plant will keep you happy in the end. LOL Good luck! TWW
You could fill it with autos in fairly big pots and harvest sooner if your looking for yields. Most autos you can pull 2oz off if you a grasp of how to grow them.