Cacamal is right all the factors are very important & the 600 watt will give u more light penetration. And of course the strain is a factor. In regards the height, I flower them under 1000watt s & some strains can get 6ft. tall+..But I have the room to be able to rise the lights. And long as u dont over crowd it should be fine. I tend to prune the lower smaller stuff off the bottoms so that upper buds can get real nice. Ive done both & get better results that way. Just from a lot of experience. I definity think u will be happier with a 600 watt. Peace & happy Gardening.