i have a 4" high velocit fan cooling 2 1000w in a 8wx11lx8h room. try to mount your carbon filter in an "exhaust" position. i made a enclosed box to hold the filter(kind of like a speaker box/particle board), mounted that in the window seal and sealed the window light & air tight. Window is open 3 inches with miniblinds, box is vented to the outside. from the outside , all you see is miniblinds and window screen. connect your ducting from the filter to the fan so the fan is "pushing" air out the filter( make this run of ducting as short as possible. Next run you ducting to the light( now your fan is sucking air through the light). This does a couple things , all the little seams and holes in the light hood are now little vacumn's instead of hot air leaks. I leave 1 side of the light ducting open to room temp, this helps to remove heat from around the light. you should also have an exhaust fan as high in the room as possible, i put mine directly over my lights.
mine flowsas follows; outside<filter<fan<"Y" adapter<2-1000w sunsystem sealed hoods< open to room(< direction of air flow). I can REST my hand on top of my hoods after thy have been on 16-18 hours. plus my room is staying about 72-76f. heres a cople picture of the filter box. i found out the hard way its better to suck air through your lights that to try and push air through.
Vortex Powerfans 6" Inline Fan- 449CFM may have 20 ft of exhaust and using a carbon filter + cooling 400Wor 600W not sure. 
