I would also skip to a single 1000. 5' tall plants require the higher penetration a single 1000w light can give and the yield will be incredible. That's how you grow colas bigger than your arms. If you can afford two 400's a single 1000 is in your range.
Kingkush your grow looks great but I see room for improvement. You would also benefit from 1000 or two of them. Your plants are tall and more penetration is key. Each leaf light passes through takes away 15% of the light going to a leaf below it, and so on and so forth. Look how little light penetration you are getting, more intensity means longer fatter colas and not so much wasted area on the bottom. Also, not trying to nitpick but that space all around your grow, do you leave it that way? You should have it more closed in with reflective material closer to the light, just hang a curtain of mylar if nothing else. (Sorry, you are doing great as is and obviously know what you're doing I'm just saying it may not be the best example to grow by.) You would really up your yield but maybe you already grow more than you care about...