Damn that sucks hydrokron....were your nirvana's feminized? 1 of my 4 (a SW) is a lot smaller than the others [for reasons unknown at the moment] but it seems to be good now. Also, the first set of leaves on both Snow Whites were really awkward looking.
As for your set-up...I'm not sure which is better (having the fan in the attic or in the room) but I'm going to go with it in the attic because I think that will be the most stealth-like (noise).
Valueline 6 Inch Centrifugal Inline Fan - Businesslights.com
That's the fan I bought. I have a 6" duct fan (160cfm stand-alone) that will be exhausting my veg room in the summer (but right now its too cold to do that). I also bought 2 fan speed controllers. We'll see how it works. My initial plan was/is to have air from the room get pulled thru the carbon filter, thru any tubing if necessary, thru the aircooled hood, up thru the top of the grow closet (thru tubing), through the fan, then out the attic.