Your not gonna like this answer, but obviously you need ducted hoods for that set up with 6x600 in one room. I'd go with two chains of exhaust for each fan at 900 or so CFM. Shit man I'm running 2200 in a smaller space, with far less overall exhaust than you, but with three cool tubes (2x600, 1X1k). Sure I'm struggling with temps during this hot ass summer, but still never over 31 degrees. All your theorizing does not take into account the actual air flow of the room dude!! Forget what the fan "can" do. Your room is not some featureless wind tunnel, the air flow will not be "optimal" or completely controlled. Venting the actually lights however is a dramatic improvement. When you vent your lights you are 100% oppositely moving the hottest air out of that room in the faster way possible, despite any other factors (room shape, angles, air flow,obstructions, etc). That's my opinion.I'd go ahead spend the 1500 bucks to get six nice hoods. Those ones yo uhave can be used for vegging (maybe not all six, lol)