I'm not really gonna read this thread, just because I find myself repeating the same exact thing over and over again.
Light penetration isn't the only factor in growing. If you cannot dissipate the heat, who cares what light your running with.
1000W magnetic ballast draws almost 1200W. You can buy a splitter and run 2 600W lights off of the 1 magnetic ballast (If your concerned about footprint)
Your electrical load is a factor too, you can't (well, shouldn't) run 2 1000w lights off of a single breaker when using 120v wiring. You can run 2 600's easily though.
Take it from someones personal experience. I grow in hydro because I did the dirt thing and am onto bigger and better things. People compliment the taste of soil grown.. but, I could care less about the taste if there's a production increase. Hydro tastes just fine to me. Show me the production numbers. That's why I also went with CO2. The numbers vs. investment cost do all the talking.
I did the 400, 600, and 1000W. 1000W are the way to go. If you want side lighting or supplemental lighting, get some 400's to go with them, so you can run 1400w on one circuit. (120v)
I also run 1000's because the growth rate and nug density, overall, seems to be better.
You'll fight heat a lot more with 1000's vs. 600's. With an open reflector, expect about a 1F degree temperature rise per 100W. 100W = +1F (depending on the size of your room obviously, im referring to a 4x8x7 space)