that is what i said but yea it doesn't really make sense when I read it. Basically I would always use 600's no matter what the setup as long as there was enough space. Since here we are talking about using an air cooled hood then the heat difference generated inside the tent between a 400 and a 600 would be negligible, especially if the ballast is located outside the tent and assuming the light is well air-cooled.
A 400 draws 400 watts and produces roughly 50,000 lumens
A 600 draws 600 watts and produces roughly 95,000 lumens
The 600 is producing 158.3 lumens per watt.
The 400 is producing 125 lumens per watt. Since it is producing less lumens per watt it is generating more heat per watt proportional to the efficiency lost. It has been explained to me that this is the reason 600 watt lights are more expensive than 400 watt lights, they are more efficient. Since 1,000 watt lights are (edit: less) efficient as 600 watt lights and a user gains no additional watt to lumen production, 1,000 watt setups are pretty much the same price as 600 watt setups. Since there is no more efficiency and since multiple light sources are always better than single point light sources, I will always use chains of 600's instead of 1000's. For example now I use two 600's even though my area would have enough lumens with just one 1,000.