Quick question.
If you had a 10x10 flowering room, would you rather have one 1000watt HPS or two 400watt HPS's?
I know the standard Lumen's for a 1000watter is about 140,000 to 150,000 and the standard for 400watters is about 45,000-55,000.
So strictly by lumens it is a no brainer. Go with the...