Supposedly 600 watters are the most efficient lumen-per-watt wise, also I would get two 400w or two 600w instead of one 1000w because you never know what your future plans might be and when you want to seperate them say to flower one while another vegges you can do so. The only pitfall would be that two units might cost you a bit more. You can't put two different units in a grow room that small but think about it, you can flower and veg another at the same time. Peace