Thats a damn nice cab. I wanted to build one myself but dont have the tools/time to do it. i ended up buying one just like that at homedepot. i am also setting up my lights and vent for this cab to have it ready for my clones by the end of Aug. I have a 400 hps with the hortilux bulb that I will be putting in the cab. I built a home made cool tube using a duct fan off of ebay ($30) and a glass tube I got from michaels for about 5 bucks(look in the candle section) This drastiacally lowered my temps in my other cab so Im assuming that this will be even better in a bigger cab. Im also thinking in addition to the cool tube i am gonna install a small extractor fan at the very top of the cab(bathroom fan). I think they start at $15 at homedepot and go up depending on cfm and noise. Im hoping that the cool tube combined with the top fan should give me more than enough ventillation to keep my temps manageable. I would def say that you should go for the 400w. That cab is huge and anything less would seem like wasted potential. Just make sure that you make a cooltube and pipe out the air and you should be fine. Good luck on the cab. -Diz:rasta: