I had the same setup as you. I started with several 400's and then I got a deal on 8 1K HPS ballasts. BELIEVE ME, go with the 1K!! I now veg with the 400's but flower with the 1K BEASTS!!!
Where did these values come from?The example room has an 8.2ft (2.5m) ceiling height so we can use the 1000W lights, as long as the plans don’t get bigger than 5ft (1.5m) which is fine for most plants. Indoor plants want to be short and wide to make the most of the light available. The distance between the light and the canopy that most growers follow are:
1000W = 39-31 inches (100cm-80cm)
600W = 31-24 inches (80-60cm)
400W = 24-16 inches (60-40cm)
What square footage are we talking about?
Simon
http://urbangardenmagazine.com/2010/07/planning-your-grow/Where did these values come from?
Simon