3 x 3 means you have a 9 square foot growing area. Optimal is 7,000 to 7,500 or higher lumens per square foot. So 9 x 7,000 = 63,000 Lumens for optimal growth. Some of the better HID's can produce 125 lumens per watt. Now after all the numbers, I would go with a 400w light and make sure to kept ventilation and cooling good.

GTD