The 600 does a great job on a crop.But if you have means to run 1000,with good ventilation,You'll have denser budding.
This is my concern, but I am also looking for efficiency.

I am barrowing a 1000 ballast now, and I have a 400 ballast, but I am looking at either buying my own 1000 or getting this dual still... I really dont need to Veg with these lights since I have two systems (I run a T5 400W on my veg and then the other setup in my flower).